i^ilijiiitiil! 


iililiiliiilillliiliiili 


r 
It' 


im\ 


ti 


Nortlj  Olarnltna  S^Mt 


This  book  was  presented  by 

Dr.    Z.    P.    Hetoalf 

QH366 
J67 


NORTH   CAPUI  INA    STATE    UNIVEPSIIY    LIBRARIES 


S00495423    R 


<./ 


144369 


This  book  may  be  kept  out  TWO  WEEKS 
ONLY,  and  is  subject  to  a  fine  of  FIVE 
CENTS  a  day  thereafter.  It  is  due  on  the 
day  indicated  below: 


1Apr'59f 


f>fW>r.ft»liiiif»ii|i?fj?rw 


50M— May-54— Form    3 


EVOLUTION   AND   ANIMAL   LIFE 


2 


Plate  I.  — Four  species  of  American  orioles  :  1,  Nelson's  oriole.  Icterus 
nelsoni ;  2,  orchard  oriole,  I.  spurius;  3,  Baltimore  oriole,  /.  gal- 
bula;  4,  Bullock's  oriole,  /.  hullocki.      (From  specimens.) 


EYOLUTION  AND  ANIMAL  LIFE 


AN  ELEMENTARY   DISCUSSION  OF 

FACTS,   PROCESSES,   LAWS   AND  THEORIES    RELAriNG 
TO  THE   LIFE   AND    EVOLUTION    OF  ANIMALS 


BY 


DAVID    STARR    JORDAN 

PRESIDENT  OF  LELAND  STANFORD   JUNIOR  UNIVERSITY 

AND 

VERNON    LYMAN    KELLOGG 

PROFESSOR  OF  ENTOMOLOGY,    AND  LECTURER   IN   BIONOMICS 
IN  LELAND  STANFORD  JUNIOR  UNIVERSITY 


Time,  whose  tooth  gnaws  away  everything 
else,  is  powerless  against  Truth.— Huxley. 


NEW   YORK    AND    LONDON 

D.  APPLETON   AND   COMPANY 

1920 


r^j^a^%    *^.^.a.d 


Copyright,  1907,  by 
D.  APPLETON  AND  COMPANY 


Printed  in  the  Umted  States  of  America 


PREFATORY  KOTE 


In  the  present  volume  the  writers  have  tried  to  give  a  lvK-i<I 
elementary  account,  in  limited  space,  of  the  processes  of  evo- 
lution as  they  are  so  far  understood.  We  have  turned  to  ani- 
mals for  illustrative  purposes,  nearly  to  tlie  exclusion  of  refer- 
ences to  plants,  simply  because  both  authors  are  zoologists 
and  have  made  use  of  the  facts  most  familiar  to  them. 

The  book  is  composed  primarily  of  the  substance  of  a  univer- 
sity course  of  elementary  lectures  delivered  jointly  })y  tlie 
authors  each  year  to  students  representing  all  lines  of  college 
work.  This  fact,  and  the  desirable  limiting  of  the  book  to  a 
convenient  size  for  the  general  reader  and  student,  account  for 
the  extremely  laconic  treatment  of  various  important  moot 
points  concerning  the  evolution  mechanism,  and  for  the  omission 
of  certain  discussions  which  otherwise  might  well  have  Ijeen 
included.  But  on  the  whole  the  authors  feel  that  the  interested 
general  reader  will  find  this  small  volume  a  fairly  compreliensive 
introduction  to  our  present-day  knowledge  of  the  factors  and 
phenomena  of  organic  evolution. 

To  the  general  reader  we  may  perhaps  witli  propriety  ad- 
dress the  following  words,  used  to  the  students  in  the  opening 
lecture  of  the  course: 

We  cannot  talk  long  without  saying  something  others  do 
not  beheve.  Others  cannot  talk  long  without  saying  something 
we  do  not  believe.  We  wish  you  to  accept  no  view  of  ours 
unless  you  reach  it  through  your  own  investigation.  What  we 
hope  for  is  to  have  you  think  of  these  things  and  find  out  for 

yourselves. 

D.  S.  J. 

V.  L.  K. 

Leland  Stanford  Junior  University, 
March  30,  1907. 

141369 


TABLE   OF  CONTENTS 


CHAPTER  I.— Evolution  Defined. 

Organic  evolution  and  bionomics,  1;  Meaning  of  evolution,  2; 
Encasement  theory,  2;  Theory  of  epigcnesis,  3;  Evolution  of  the 
species  or  transmutation,  3;  Cosmic  evolution,  4;  Spencer's  fonn- 
ula  of  evolution,  5;  Biologic  evolution  and  cosmic  evolution  not 
the  same,  6;  Usefulness  of  the  term  bionomics,  7;  The  flux  of  na- 
ture, 7;  Comprehensiveness  of  the  science  of  organic  evolution,  8; 
The  immanence  and  permanence  of  law,  9;  Evolution  not  neces- 
sarily progress,  10;  Theory  of  descent,  10. 

CHAPTER   II. — Variety  and  Unity  in  Life. 

Range  of  variety,  12;  Meaning  of  species,  13;  Number  of  si>ecies, 
14;  Extinct  species,  16;  Changes  of  species  with  time  and  place, 
18;  Variety  in  life  a  factor  in  the  history  of  the  globe,  21;  Unity 
m  life,  22. 

CHAPTER  III. — Life,  Its  Physical  Basis  and  Simplest  Expres- 
sion. 

Live  things  and  lifeless  things,  25;  The  basic  distinction  between 
life  and  non-life,  26;  Protoplasm,  26;  Chemical  make-up  of  proto- 
plasm, 27;  Physical  make-up  of  protoplasm,  28;  The  cell.  30:  The 
simplest  animals,  32;  Differentiation  and  animal  types,  32;  The 
genealogical  tree,  36;  Primary  conditions  of  life,  38:  Origin  of  life, 
41;  Spontaneous  generation,  42;  Where  did  life  begin  on  the 
earth,  47. 

CHAPTER   IV.— Factors  and  Mechanism  of  Evolution. 

The  fact  of  descent,  48;  Darwinism  not  synonymous  with  i\o- 
scent,  49;  Factors  in  descent,  49;  Variation,  .")0;  Selection,  ol: 
Prodigality  of  production,  52;  Heredity,  53;  Isolation,  53;  .Mutii- 
tion,  54;  Orthogenesis,  55:  Lamarckism  and  inheritance  of  ac- 
quired characters,  55;  Adaptation.  56. 

Yii 


viii  TABLE  OF  CONTENTS 

CHAPTER  V. — Natural    Selection  and   Struggle   for   Exist- 
ence: Sexual  Selection. 

Natural  selection  the  chief  determining  agent  in  adaptation,  57; 
Adaptation  to  conditions  of  life,  58;  The  crowd  of  animals,  59; 
Reproduction  by  multiplication,  59;  Numbers  of  individuals  al- 
most stationary,  60;  Struggle  for  existence,  60;  Discriminate 
death,  61;  Natural  selection,  62;  Interdependence  of  species,  63; 
Animal  and  plant  invasions,  64;  Doctrine  of  Malthus,  67;  Limits 
to  the  capacity  of  natural  selection,  68;  Survival  of  the  existing, 
69;  Actual  standing  of  Darwinism,  70;  Secondary  sexual  dif- 
ferences, 71;  Classification  of  secondary  sexual  characters,  72; 
Theory  of  sexual  selection,  75;  Criticisms  of  the  theory,  77;  The 
sexual  selection  theory  largely  discredited,  78. 

CHAPTER   VL— Artificial   Selection. 

Natural  selection  and  artificial  selection,  80;  Steps  in  the  pro- 
duction of  new  races,  81;  Selected  traits  quantitative,  81;  Race 
traits  qualitative,  84;  Hybridization,  88;  Plant  amelioration,  90; 
Work  of  Luther  Burbank,  90;  Panmixia,  or  cessation  of  selection, 
104;  Reversal  of  selection,  104;  Transmission  and  heredity,  105; 
Artificial  selection  and  natural  selection,  analogous  processes, 
106;  Race-forming  by  sports,  107. 

CHAPTER  VII. — Various    Theories    of    Species-forming    and 
Descent  Control. 

Segregation  of  isolation,  108;  Geographic  and  physiologic  iso- 
lation, 109;  Romanes's  championship  of  physiologic  isolation,  109; 
The  Lamarckian  theory  of  species-transformation.  111;  Ortho- 
genetic  evolution,  112;  Species-forming  by  mutation,  114;  The  un- 
known factors  of  evolution,  115. 

CHAPTER   VIII. — Geographic  Isolation  and  Species-forming. 

Migration  and  faunal  distribution,  117;  Closely  related  species 
not  found  in  the  same  region,  but  in  contiguous  regions,  120;  The 
American  warblers,  120;  Barriers,  122;  The  Hawaiian  Drepanidse, 
124;  Adaptive  and  non-adaptive  characters,  127;  The  American 
orioles,  128;  Species  traits  not  necessarily  useful,  129;  The  persist- 
ence of  the  sufficiently  fitted,  130. 

CHAPTER   IX. — Variation  and  Mutation. 

Actuality  and  extent  of  individual  variation,  131;  Darwin's 
laws  of  variation,  137;  Quetelet's  determination  that  fluctuating 
variation  follows  the  law  of  probabilities,  140;  Discontinuous  varia- 


TABLE   OF  CONTENTS  ix 

tion,  141;  Discontinuous  and  continuous  variation,  141;  Congeni- 
tal and  acquired  variation,  142;  Determinate  variation,  loO;  Thi.' 
causes  of  variation,  154,  156;  Variation  as  related  to  amphimixis 
and  parthenogenesis  as  mutations  of  de  Vries,  154. 

CHAPTER  X.— Heredity. 

Hereditary  variancy  defined,  163;  Atavism  or  reversion,  166; 
Telogony,  166;  Prenatal  influences,  167;  Not  all  transmission  is 
heredity,  168;  Determination  of  sex,  170;  Homologies  and  anaU)- 
gies,  172;  Vestigial  organs,  174;  Significance  of  vostiginl  organs, 
181;  Heredity  and  its  "laws,"  181;  Galton's  law  of  ancestral  in- 
heritance, 184;  Mendel's  law  of  alternative  inheritance,  187; 
Modification  of  Mendelism,  188. 

CHAPTER  XI. — Inheritance  of  Acquired  Characters. 

The  Lamarckian  principles  of  evolution,  196;  Neo-Lamarckism 
and  Neo-Darwinism,  197;  Acquired  characters,  198;  Effects  of  use 
and  disuse,  199;  Environmental  modifications  not  inherited,  200; 
Examples  of  non-inheritance  of  acquired  characters,  201 ;  Heredity 
unproved,  203;  Convergence  of  characters  and  parallelism,  204; 
Actual  effects  of  environment,  205;  Ontogenetic  species,  206. 

CHAPTER  XII. — Generation,  Sex,  and  Ontogeny. 

Generation  and  ontogeny,  211 ;  Spontaneous  generation  or  abio- 
genesis,  212;  Simplest  modes  of  generation,  213;  Parthenogenesis, 
215;  Differentiation  of  reproductive  cells,  217;  Simplest  many- 
celled  animals,  218;  Effects  of  sex,  220;  Sex  dimorphism.  221: 
The  life  cycle,  223;  The  egg,  224;  Numbers  of  young,  225;  Em- 
bryonic and  post-embryonic  development,  227;  Developmental 
stages,  229;  Continuity  of  development,  231;  Metamorphosis  or 
apparent  discontinuity,  234;  Significance  of  facts  of  develop- 
ment, 234;  Divergence  of  development,  234;  The  duration  of 
life,  240;  Death,  241. 

CHAPTER    XIII.— Factors    in    Ontogeny,    and    Experimental 
Development. 

Processes  in  ontogeny,  244;  Extrinsic  and  intrinsic  factors,  245; 
Mechanism  versus  vitalism,  246;  Functions  of  protoplasm.  247; 
Ultimate  structure  of  protoplasm,  248;  Theories  of  organic  units, 
250;  Cell  division,  251;  Mitosis,  or  karyokinesis,  252;  Somatic  and 
germ  tissues,  257;  Reproduction  in  i)roto7.oa.  2()0;  Maturation, 
264;  Fertilization,  267;  Cleavage,  269:  Reduction  of  the  chromo- 
somes, 269;  Preformation  versus  epigenesis,  276;  Examples  giving 


X  TABLE   OF  CONTENTS 

evidence  for  each,  278;  Mechanism  versus  vitahsm,  281;  Artificial 
parthenogenesis,  283;  Regeneration  and  regulation,  285. 

CHAPTER  XIV.— Paleontology. 

Fossils  and  thei/  significance,  289;  Fossil-bearing  rocks  and 
their  origin,  292;  Geological  epochs,  296;  Conditions  of  extinct 
life,  297;  Divergent  types  and  synthetic  types,  299;  Parallelism 
between  geologic  and  embryonic  series,  300;  Orthogenesis,  301; 
Significance  in  evolution  of  the  facts  of  paleontology,  301 ;  Dur- 
ation in  time  of  species,  302;  History  of  the  vertebrates,  305; 
Man,  307. 

CHAPTER  XV. — Geographical  Distribution. 

Zoogeography,   309;   Relation  of  species  to  geography,   311 
Laws  of  distribution,  314  ;  Species  debarred  by  barriers,  315 
Species    debarred   by. inability  to    maintain   their  ground,  315 
Species  altered  by  adaptation  to  new  conditions,  315;   Effects  of 
barriers,  316;  Faunas  and  faunal  areas,  316;  Remains  of  animal 
life,  322;  Subordinate  remains  of  provinces,  323;  Faunal  areas  of 
sea,  323 ;  Analogies  between  language  and  fauna,  325 ;  Geographic 
distribution  and  the  theory  of  descent,  326. 

CHAPTER  XVL— Adaptations. 

The  principle  of  fitness  and  general  adaptations,  327;  Origin 
of  adaptations,  327;  Types  and  classification  of  species  adapta- 
tions, 328;  Adaptations  for  food-securing,  329;  Adaptations  for 
self-defense,  330;  Adaptations  brought  about  by  rivalry,  331; 
Adaptations  for  defense  of  young,  338;  Special  adjustments  to 
surroundings,  343. 

CHAPTER  XVIL — Parasitism  and  Degeneration. 

Parasitism  defined,  347;  Kinds  of  parasitism,  348;  Simple 
structure  of  parasites,  350;  Gregarina,  351;  Parasitic  hemospor- 
idia:  the  cause  of  malarial  fevers,  351 ;  Tapeworm  and  other  flat 
worms,  354;  Trichina  and  other  round  worms,  355;  Sacculina,  358; 
Parasitic  insects,  359;  Parasitic  vertebrates,  361 ;  Parasitic  plants, 
362;  Degeneration  through  quiescence,  363;  Degeneration  through 
other  causes,  363;  Immediate  causes  of  degeneration,  366;  Ad- 
vantages and  disadvantages  of  parasitism  and  degeneration,  36. 

CHAPTER  XVIII. — Mutual  Aid  and  Communal  Life  among  Ani- 
mals. 

Man  not  the  only  special  animal,  369;  Animal  societies,  369; 
Commensalism,  370;  Symbiosis,  373;  Symbiosis  between  animals 


TABLE  OF  CONTENTS  xi 

and  plants,  376;  Social  life,  grcgariousncss,  380;  Solitary  and  com- 
munal bees  and  wasps,  383;  The  honey-boe  community,  387;  Ants, 
391;  Termites,  394;  Division  of  labor  the  basis  of  communal  life, 
395;  Advantages  of  communal  life,  397. 

CHAPTER  XIX. — Color  and  Pattern  in  Animals. 

Color  among  animals,  398;  Protection  by  color,  400;  Protection 
.f  color,  402;  Significance  of  color  and  pattern,  404;  Table  of  in- 
sect colors,  405;  General  protective  resemblance,  400;  Variable 
protective  resemblance,  407;  Special  protective  resemblance,  411 ; 
Warning  colors,  416;  Terrifying  appearances,  418;  Directive  col- 
oration, 419;  Recognition  marks,  420;  Mimicry,  421 ;  Criticism  and 
general  considerations  of  the  theory  of  protective  and  mimicking 
color  pattern,  424. 

CHAPTER  XX. — Reflexes,  Instinct,  and  Reason. 

Irritability,  426;  Nerve  cells  or  fibers,  427;  Brain  or  sensorium, 
427;  Mechanical  reflexes,  428;  The  tropism  theory,  429;  The 
theories  of  the  method  of  trial  and  error,  429;  Instincts,  430;  In- 
stincts of  feeding,  432;  Instincts  of  self-defense,  433;  Instinct  of 
play,  435;  Climatic  instincts,  436;  Environmental  instincts,  438; 
Instincts  of  courtship,  438;  Instincts  of  reproduction,  439;  In- 
stincts concerned  with  the  care  of  the  young,  439;  Variability  of 
instinct,  442;  Reason,  443;  Mind,  448. 

CHAPTER  XXL— Man's  Place  in  Nature. 

Post-Darwinian  conception  of  humanity,  452;  Man's  place 
among  the  other  animals,  453;  Classification  of  the  primates,  455; 
Evidences  from  comparative  anatomy  of  man's  rehition  to  lower 
animals,  456;  Special  physiological  evidence,  457;  Evidence  from 
embryology,  460;  Evidence  from  paleontology.  401;  (\)nchLsionH 
from  ethnology,  462;  The  earliest  man,  464'  The  genealogy  of 
man,  466;  Theology  and  Darwinism,  467. 


EVOLUTION   AND   ANIMAL   LIFE 


CHAPTER  I 
EVOLUTION   DEFINED 

Grau,  theurer  Freund,  ist  alle  Theorie, 
Und  griin  des  Lebeiis  gold'ner  Bauin. 

— ClOETHE. 

Men  of  science  repudiate  the  opinion  that  natural  hnvs  are  rulers 
and  governors  of  nature,  looking  with  suspicion  on  all  "  necessary  "  and 
universal  laws. — Brooks. 

This  volume  treats  of  the  elements  of  the  science  of  Orj^anic 
Evolution.  To  this  science  belongs  the  consideration  of  tlie 
forces  which  govern  the  changes  in  organisms.  It  includes  the 
influences  w^hich  control  development  in  the  individual  and  in 
the  species  wdiich  is  the  succession  of  individuals,  together  with 
the  laws  or  observed  sequences  of  events  which  development 
exhibits.  From  another  point  of  view,  this  is  the  science  of' 
life — adaptation.  The  term  Bionomics  (fitds,  Ufe,  vo'/xos,  order 
or  custom),  first  suggested  by  Prof.  Patrick  Geddes,  is  essen- 
tially equivalent  to  the  older  term  Organic  Evolution,  the 
science  of  the  facts,  processes,  and  laws  involved  in  the  nuitation 
of  organisms.  For  many  reasons,  this  new  name,  Bionomics, 
w^ith  its  technically  exact  meaning,  should  be  preferred  to  the 
phrase  Organic  Evolution,  as,  unlike  the  latter,  it  involves  no 
philosophic  assumptions. 

That  organs  and  organisms  do  change  from  day  to  day,  and 
place  to  place,  and  from  generation  to  generation  is  an  observed 
fact,  -which  now^  admits  of  no  doubt.  The  orderly  ari-angement 
of  our  knowledge  of  this  process  constitutes  a  branch  of  science. 
To  use  the  word  evolution  in  regard  to  this  jirocess  is  to  use  a 
philosophic  term  in  connection  with  a  group  of  scientific  facts. 
For  the  word  evolution  means  unrolling.    It  carries  the  thought 

1 

D.  H.  HILL  LIBRARY 
North  GH-olina  State  College 


2  EVOLUTION  AND  ANIMAL  LIFE 

that  something  which  was  previously  hidden  is  now  brought  to 
Hght.  This  leads  naturally  to  the  philosophic  suggestion  that 
whatever  is  evolved  must  be  previously  involved.  This  may 
be  true  as  a  matter  of  words,  but  not  necessarily  so  as  a  matter 
of  fact,  unless  we  reduce  these  words  to  the  simple  meaning 
that  the  actual  now  must  have  been  the  possible  before;  what- 
ever actually  takes  place  was  a  possibiUty  before  it  happened. 

The  word  evolution,  then,  belongs  to  philosophy  rather  than 
to  science.  In  the  philosophy  of  nature  the  idea  that  present 
conditions  are  brought  about  through  unrolling  or  unveihng 
has  had  a  long  existence.  The  word  evolution  has  been  fre- 
quently applied  to  the  process  of  growth  and  maturity  of  the 
individual  animal  or  plant,  and  again  to  the  process  of  deriva- 
tion of  species  from  ancestral  organisms,  and  again  to  the  pro- 
gressive changes  in  the  forms  of  inorganic  bodies,  as  planets 
or  mountains.  Each  one  of  these  meanings  is  essentially  dis- 
tinct from  the  others,  and  each  is  distinct  from  the  theory 
of  evolution  which  existed  in  the  dawn  of  biological  science. 
When  men  first  began  to  notice  the  changes  in  the  animal 
embryo,  through  which,  from  the  formless  egg,  little  b}^  httle, 
the  individual  was  built  up,  becoming  at  each  stage  of  the 
process  larger,  more  speciahzed,  and  more  like  the  parent 
from  Avhich  it  sprang,  it  was  natural  to  regard  this  process  as 
an  unrolling.  It  was  natural,  too,  to  suppose  that  the  egg 
was  not  really  formless,  but  that  the  beginnings  of  each  part 
of  the  final  organism  existed  within  it  in  fact,  if  we  could 
see  them.  Hence  evolution  took  the  form  of  a  theory  of 
encasement.  Men  imagined  that  the  egg  of  the  chicken  con- 
tained a  minute  chicken,  and  that  within  this  chicken  were 
the  germs  of  the  eggs  the  future  hen  would  bear;  and  again, 
that  encased  within  each  of  these  eggs  was  an  endless  series  of 
the  eggs  and  chickens  of  all  the  future.  In  like  fashion,  men 
conceived  that  in  the  small  human  egg  were  the  bodies  and 
embryos  of  countless  future  generations.  In  some  theories, 
this  idea  of  encasement  was  applied  not  to  the  egg,  but  to  the 
male  germ,  the  homunculus  or  minute  man  in  whom  the  gener- 
ations of  the  future  were  enfolded  and  from  which  they  un- 
rolled. 

The  perfection  of  the  microscope  as  an  instrument  of  pre- 
cision did  not  verif}^  these  theories  of  encasement.  The  egg 
still  appeared  essentially  formless,  a  mass  of  undifferentiated 


EVOLUTION   DEFINED  3 

protoplasm,  or  at  least  without  traceable  lineaments  of  the 
future  embryo.  It  was  a  single  cell,  apparently  essentially  like 
any  other  cell,  a  single  one  of  the  units  of  structure  of  whicli 
living  organisms  are  made. 

Thence  arose  the  theory  of  upbuilding  or  epigenesis  {t-rri, 
upon,  yei/€o-t5,  birth)  of  organisms,  by  the  addition  of  cell  u})()n 
cell,  to  the  original  germ  or  egg.  Each  egg  cell  by  segmentation 
divides  into  two  daughter  cells,  and  these,  through  the  influence 
of  heredity,  naturally  arrange  themselves  so  that  a  new  organ- 
ism is  formed  similar  to  the  parent  organism.  It  was  recognized 
that  the  form  was  predetermined  by  the  ancestry,  but  no 
longer  that  the  embryo  was  literally  released  from  encasement 
within  the  structure  of  the  egg.  The  evolution  of  the  individual 
is  thus  conceived  as  the  realization  of  an  hereditary  tendency. 

But  "hereditary  tendency"  is  again  a  metai)horical  ex- 
pression. In  biology,  we  know  no  "influence''  or  "tendency" 
which  is  not  localized  somewhere.  Any  act  or  modification  of 
an  act  is  a  function  of  some  particular  organ.  To  account  for 
the  Ukeness  involved  in  the  facts  of  heredity,  we  must  expect 
to  find  some  form  of  organic  mechanism. 

Such  mechanism  must  exist  within  the  germ  cell  itself,  and 
its  existence  as  the  "physical  basis  of  heredity"  is  now  well 
estabUshed.  In  a  later  chapter  we  shall  discuss  the  nature 
of  this  physical  basis,  the  structures  within  the  nucleus  of  the 
germ  cell  which  control  or  preside  over  the  develoi)ment  of  the 
individual.  From  our  knowledge  of  the  operation  of  the  cell 
in  heredity  we  recognize  the  facts  of  epigenesis,  and  witli  these 
a  theory  of  individual  evolution,  much  more  subtle  than  the 
old  theory  of  encasement. 

We  may  therefore  still  imagine  the  maturing  of  the  individ- 
ual organ  as  a  process  of  evolution,  or  unrolling,  of  the 
hereditary  plan  as  hidden  in  the  structure  of  its  colls.  We  may 
also  speak  of  the  same  process  as  a  development.  To  envelop 
is  to  make  snug.  Development  is  its  opposite.  To  develop 
is  to  make  free  or  independent. 

From  the  evolution  of  the  individual  it  is  natural  to  extend 
the  use  of  the  word  evolution  or  the  word  development  to  the 
changes  which  characterize  the  history  of  a  species  or  other 
group  of  animals  or  plants,  a  process  which  has  also  been  vi\\M 
transformism  or  transmutation.  This  word  transmutation  de- 
scribes   the    process  more    Uterally  than   cither  evolution   or 


4  EVOLUTION  AND  ANIMAL  LIFE 

development.  That  species  do  change  their  structure  with 
time  or  with  space  is  a  matter  of  common  scientific  observation. 
With  the  lapse  of  time,  generation  following  generation,  direct- 
ive influences  combine  to  modify  the  line  of  descent.  With 
the  separation  of  individuals  by  barriers  of  land  and  water 
and  varying  climate,  differing  lines  of  descent  are  brought  into 
existence.  The  fact  of  descent  with  modification  large  or  small 
is  a  matter  of  common  knowledge  in  the  biology  of  to-day,  veri- 
fied in  the  hundreds  of  thousands  of  species  of  organisms  now 
known  and  classified.  To  call  this  transmutation  of  species  is 
but  to  state  the  fact.  To  call  it  evolution  is  to  suggest  a  theory 
that  all  these  changes  are  but  the  unrolling  of  the  plan — a  move- 
ment toward  some  predetermined  end.  That  this  is  true  we  have 
no  means  of  knowing,  and  the  results  as  they  appear  to  us  seem 
to  be  determined  by  proximate  causes  alone.  Among  these 
proximate  causes  are  differences  in  structiu^e  and  in  degrees  of 
adaptability  among  individuals,  the  operation  of  the  rule  of 
the  survival  of  the  best  adapted,  the  inheritance  by  individuals 
of  the  traits  of  the  immediate  ancestry,  and  the  effects  of  cli- 
matic changes,  and  of  migrations  hampered  and  unhampered 
by  the  presence  of  physical  barriers.  The  effects  of  influ- 
ences like  these  are  considered  by  most  TVTiters  as  the  es- 
sential elements  in  "organic  evolution."  But  a  few  writers 
give  external  iiifluences  a  secondary  place,  confining  the  term 
evolution  solely  to  the  results  of  causes  resident  within  the 
individual. 

Speaking  broadly  we  find  as  a  fact  that  transmutation  of 
species  through  the  geologic  ages  has  been  accompanied  by 
increasing  divergence  of  type,  by  the  increased  specialization 
of  certain  forms,  and  by  the  closer  and  closer  adaptation  to 
conditions  of  hfe  on  the  part  of  the  forms  most  highly  special- 
ized, the  more  perfect  adaptation  and  the  more  elaborate 
specialization  being  associated  with  the  greatest  variety  or 
variation  in  environment.  Accepting  for  this  process  the  name 
of  organic  evolution,  Herbert  Spencer  has  deduced  from  it  the 
general  law  that  as  life  endures  generation  after  generation,  its 
character,  as  shown  in  structure  and  function,  undergoes  con- 
stant differentiation  and  specialization.  In  this  view,  the 
transmutation  of  species  is  not  merely  an  observed  process,  but 
a  primitive  necessity  involved  in  the  very  organization  of  life 
itself. 


EVOLUTION   DEFINED  5 

A  process  of  orderly  mutation  is  observed  not  only  in  living 
things  but  in  inanimate  ol^jects  as  well.  The  features  of  the 
surface  of  the  earth  pass  through  a  slow  process  of  unrolling — 
from  primitive  chaos  to  the  diversified  earth  of  to-day.  Mnu'i- 
festly  we  cannot  imagine  a  homogeneous  earth  which  could 
forever  retain  its  homogeneous  condition.  At  least  our  universe 
and  our  earth  have  not  done  so.  A  cooling  earth  must  lose 
its,  perfect  rotundity,  its  surface  nnist  become  (hvcrsificd,  its 
relation  to  the  sun  must  cause  its  equator  to  differ  from  its 
poles.  A  single  homogeneous  form  of  life  on  this  earth  could 
not  remain  uniform  because  it  wou.ld  be  thrown  unrlor  varying 
conditions.  It  could  not  be  the  same  under  the  tropical  sun  jis 
under  the  arctic  cold,  and  the  individuals  ada})tcd  to  either 
would  tend  to  reproduce  individuals  likewise  adapted.  There 
must,  then,  exist  in  all  things  a  '^  tendency  "to  become  special- 
ized and  differentiated.  In  accordance  Avith  this  tendency,  it  is 
conceived  that  nebulous  masses  have  been  concent  rat  etl  into 
planets  and  the  generalized  creatures  of  geologic  time  have  l)een 
succeeded  by  variant  and  specialized  forms,  their  lineal  de- 
scendants. 

The  universal  formula  of  the  process  of  evolution  is  com- 
pactly stated  by  Herbert  Spencer  in  these  famous  words: 

"Evolution  is  a  continuous  change  from  indefinite  incoherent 
homogeneity  to  a  definite  coherent  heterogeneity  of  structure  and 
function,  through  successive  differentiations  and  integrations.  In 
its  phj'-sical  aspect  evolution  is  further  an  integration  of  matter '.sit h 
concomitant  dissipation  of  motion." 

This  formula  appUes  more  or  less  to  all  forms  of  orderly 
change,  that  is,  change  due  to  a  persistent  cause,  a  continuous 
force.  Tluis  solar  systems  are  conceivably  formed  from  nebuhe. 
Thus  continents  and  mountain  chains,  islands  and  river  basins 
are  shaped.  Thus  organisms  are  derived  from  parent  organisms. 
Thus  all  the  variant  chemical  elements  may  have  been  (hypo- 
thetically)  derived  through  influences  as  yet  not  even  imagined, 
from  the  unknown  and  probal)ly  unknowable  primitive  element, 
protyl.  The  general  movement  is  from  the  simple  to  tlie 
complex,  from  the  homogeneous  to  the  heterogeneous,  from 
the  inexperienced  to  the  experienced,  from  the  undivided  to 
the  divided,  from  the  inchoate  to  the  integrated.  Whatever 
2 


6  EVOLUTION  AND  ANIMAL  LIFE 

happens  in  time  or  is  encountered  in  space  promotes  evolution. 
But  the  kind  of  evolution  thus  produced  is  very  different  in 
■different  kinds  of  objects. 

Biological  evolution  and  cosmic  evolution  are  not  the  same. 
From  the  biological  side  a  certain  objection  must  be  made  to 
this  philosophical  theory  of  universal  or  cosmic  evolution.  In 
organic  and  inorganic  evolution  there  is  much  in  common  so 
far  as  conditions  and  results  are  concerned;  but  these  likenesses 
belong  to  the  realm  of  analogy,  not  of  homology.  They  are  not 
true  identities  because  not  arising  from  like  causes.  The  evo- 
lution of  the  face  of  the  earth  forces  parallel  changes  in  organic 
life,  but  the  causes  of  change  in  the  two  cases  are  in  no  respect 
the  same.  The  forces  or  processes  by  which  mountains  are 
built  or  continents  established  have  no  homology  with  the 
forces  or  processes  which  transformed  the  progeny  of  reptiles 
into  mammals  or  birds.  Tendencies  in  organic  development 
are  not  mystic  purposes,  but  actual  functions  of  actual  organs. 
Tendencies  in  inorganic  nature  are  due  to  the  interrelations  of 
mass  and  force,  whatever  may  be  the  final  meanings  attached  to 
these  terms  or  to  the  terms  matter  and  energy.  It  is  not  clear 
that  science  has  been  really  advanced  through  the  conception  of 
the  essential  unity  of  organic  evolution  and  cosmic  evolution. 
The  relatively  little  the  two  groups  of  processes  have  in  common 
has  been  overemphasized  as  compared  with  their  fundamental 
differences.  The  laws  which  govern  living  matter  are  in  a  large 
extent  peculiar  to  the  process  of  living.  Processes  which  are 
functions  of  organs  cannot  exist  where  there  are  no  organs. 
The  traits  of  protoplasm  are  shown  only  in  the  presence  of 
protoplasm.  For  this  reason  we  may  well  separate  the  evolu- 
tion of  astrononi}^,  the  evolution  of  dynamic  geology  and  of 
physical  geography,  as  well  as  the  purely  hypothetical  evolu- 
tion of  chemistry,  from  the  observed  phenomena  of  the  evolution 
of  life.  To  regard  cosmic  evolution  and  organic  evolution  as 
identical  or  as  phases  of  one  process  is  to  obscure  facts  by 
verbiage.  There  are  essential  elements  in  each  not  shared  by 
the  other — or  which  are  at  least  not  identical  when  measured 
in  terms  of  human  experience.  It  is  not  clear  that  any  force 
whatever  or  any  sequence  of  events  in  the  evolution  of  life  is 
homologous  with  any  force  or  sequence  in  the  evolution  of 
stars  and  planets.  The  unity  of  forces  may  be  a  philosophical 
necessity.     A  philosophical  necessity  or  corner  in  logic  is  un- 


EVOLUTION   DEFINED  7 

known  to  science.  We  can  recognize  no  logical  necessity  until 
we  are  in  possession  of  all  the  facts.  No  ultimate  fact  is  yet 
known  to  science. 

For  reasons  indicated  above  the  term  evolution  is  not 
w^holly  acceptable  as  the  name  of  a  branch  of  science.  The 
term  bionomics  is  a  better  designation  of  the  changing  of 
organisms  influenced  througli  unclianging  laws.  It  is  a  name 
broader  and  more  definite  than  the  term  organic  evolution,  it 
is  more  euphonious  than  any  phrase  meaning  life  adaptation,  it 
involves  and  suggests  no  theory  as  to  the  origin  of  the  })henoni- 
ena  it  describes. 

It  is  a  matter  of  common  observation  that  organisms  change 
from  day  to  day,  and  that  day  by  day  some  alteration  in  their 
environment  is  produced.  It  is  a  conclusion  from  scientific 
investigation  that  these  changes  are  greater  than  they  apiu'ar. 
Not  only  do  they  affect  the  individual  animal  or  ])lant,  but  they 
affect  all  groups  of  living  things,  classes  or  races  or  species. 
No  character  is  permanent,  no  trait  of  hfe  without  change; 
and  as  the  living  organism  and  groups  of  organisms  are  un- 
dergoing alteration,  so  does  change  take  place  in  the  objects 
of  the  physical  world  about  them.  "  Nothing  endures/'  says 
Huxley,  "save  the  flow  of  energy  and  the  rational  order  that 
pervades  it.'^  The  structures  and  objects  change  their  forms 
and  relations,  and  to  forms  and  relations  once  abandoned  they 
•never  return;  but  the  methods  of  change  are,  so  far  as  we  can 
see,  immutable.  The  laws  of  life,  the  laws  of  death,  and  the 
laws  of  matter  never  change.  If  the  invisible  forces  \\hich 
rule  all  visible  things  are  themselves  subject  to  modification 
and  evolution  w^e  have  not  detected  it.  If  these  vary,  their 
aberrations  are  so  fine  as  to  defy  human  observation  and  com- 
putation. In  the  control  of  the  universe  we  find  no  trace  of 
"variableness  nor  shadow  of  turning." 

But  the  objects  we  know  do  not  endure.  Only  tlie  shortness 
of  human  life  allows  us  to  speak  of  species  or  even  of  individuals 
as  permanent  entities.  The  mountain  chain  is  no  more  nearly 
eternal  than  the  drift  of  sand.  It  endures  beyond  the  period  of 
human  observation;  it  antedates  and  outlasts  human  history. 
So  may  the  species  of  animal  or  i)lant  outlast  and  antedate  the 
lifetime  of  one  man.  Its  changes  are  slight  even  in  the  lifetime 
of  the  race,  Thus  the  species,  through  the  persistence  of  its 
type  among  it§  changing  individuals,  has  come  to  ho  recrarded 


8  EVOLUTION   AND  ANIMAL   LIFE 

as  something  which  is  beyond  modification,  unchanging  so  long 
as  it  exists. 

"I  beheve/'  said  the  rose  to  the  hly  in  the  parable,  "that 
our  gardener  is  immortal.  I  have  watched  him  from  day  to 
day  since  I  bloomed,  and  I  see  no  change  in  him.  The  tulip 
who  died  yesterday  told  me  the  same  thing.'' 

As  a  flash  of  lightning  in  the  duration  of  the  night,  so  is  the 
life  of  man  in  the  duration  of  nature.  When  one  looks  out  on 
a  storm  at  night  he  sees  for  an  instant  the  landscape  illumined 
by  the  lightning  flash.  All  seems  at  rest.  The  branches  in  the 
wind,  the  flying  clouds,  the  falling  rain,  are  all  motionless  in 
this  instantaneous  view.  The  record  on  the  retina  takes  no 
account  of  change,  and  to  the  eye  the  change  does  not  exist. 
Brief  as  the  lightning  flash  in  the  storm  is  the  life  of  man  com- 
pared with  the  great  time  record  of  life  upon  earth.  To  the 
untrained  man  who  has  not  learned  to  read  these  records, 
species  and  types  in  life  are  enduring.  From  this  illusion  arose 
the  theory  of  special  creation  and  permanence  of  tj^pe,  a  theory 
which  could  not  persist  when  the  facts  of  change  and  the  forces 
causing  it  canie  to  be  studied  in  detail. 

But  when  men  came  to  investigate  the  facts  of  individual 
variation  and  to  think  of  their  significance,  the  current  of  life 
no  longer  seemed  at  rest.  Like  the  flow  of  a  might}^  river,  ever 
sweeping  steadily  on,  never  returning,  is  the  movement  of  all 
life.  The  changes  in  human  history  are  only  typical  of  the 
changes  that  take  place  in  all  living  creatures.  In  fact,  human 
history  is  only  a  part  of  one  great  life  current,  the  movement  of 
which  is  everywhere  governed  by  the  same  laws,  depends  on  the 
same  forces,  and  brings  about  like  results. 

Organic  evolution,  or  bionomics,  is  one  of  the  most  com- 
prehensive of  all  the  sciences,  including  in  its  subject  matter 
not  only  all  natural  history,  not  only  processes  like  cell  division 
and  nutrition,  not  only  the  laws  of  heredity,  variation,  segre- 
gation, natural  selection,  and  mutual  help,  but  all  matters  of 
human  history,  and  the  most  complicated  relations  of  civics, 
economics,  and  ethics.  In  this  enormous  science  no  fact  can 
be  without  a  meaning,  and  no  fact  or  its  underlying  forces  can 
be  separated  from  the  great  forces  whose  interaction  from 
moment  to  mom^ent  writes  the  great  story  of  life, 

And  as  the  basis  to  the  science  of  bionomics,  as  to  all  other 
science,  must  be  taken  the  conception  that  nothing  is  due  tQ 


EVOLUTION   DEFINED  9 

chance  or  whim.  Whatever  occurs  coines  as  tlie  resultant  of 
moving  forces.  Could  we  know  and  estimate  these  forces,  we 
should  have,  so  far  as  our  estimate  is  accurate  and  our  logic 
perfect,  the  gift  of  prophecy.  Knowing  the  law,  and  knowing 
the  facts,  we  should  foretell  tlie  results.  To  be  ahle  in  some 
degree  to  do  this  is  the  art  of  hfe.  It  is  the  ultimate  end  of 
science,  v/hich  finds  its  final  purpose  in  human  conduct. 

"A  law,"  according  to  Darwin,  "is  the  ascertained  se(iuencc 
of  events. '^  The  actual  sequence  of  events  it  is,  in  fact,  but 
man  knows  notliing  of  what  is  necessary,  only  of  what  has  been 
ascertained  to  occur.  Because  human  observation  and  logic 
can  be  only  partial  no  law  of  life  can  be  fully  stated.  Ht-cau.se 
the  processes  of  human  mind  are  human,  with  organic  limita- 
tions, the  study  of  the  mind  itself  becomes  a  part  of  the  science 
of  bionomics.  For  it  is  itself  an  instrument  or  a  combination 
of  instruments  by  v/hich  we  acquire  such  knowledge  of  the 
world  outside  of  ourselves  as  may  be  needed  in  the  art  of  living, 
in  the  degree  in  which  we  are  able  to  practice  that  art. 

The  necessary  sequence  of  events  exists,  whether  we  are  able 
to  comprehend  it  or  not.  The  fall  of  a  leaf  follows  fixed  laws 
as  surely  as  the  motion  of  a  planet.  It  falls  by  chance  because 
its  short  movement  gives  us  no  time  for  observation  and  calcu- 
lation. It  falls  by  chance  because,  its  results  being  imini- 
portant  to  us,  we  give  no  heed  to  the  details  of  its  motion.  But 
as  the  hairs  of  our  head  are  all  numbered,  so  are  nunil)ored  all 
the  g^Tations  and  undulations  of  every  chance  autumn  leaf. 
All  processes  in  the  universe  are  alike  natural.  The  creation 
of  man  or  the  growth  of  a  state  is  as  natural  as  the  formation 
of  an  apple  or  the  growth  of  a  snowbank.  All  are  alike  super- 
natural, for  they  all  rest  on  the  huge  unseen  solidity  of  the 
universe,  the  imperishability  of  matter,  the  conservation  of 
energy,  and  the  immanence  of  law\ 

We  sometimes  classify  sciences  as  exact  antl  inexact,  m 
accordance  with  our  al^ility  exactly  to  weigh  forces  and  results. 
The  exact  sciences  deal  with  simple  data  accessible  and  (apable 
of  measurement.  The  results  of  their  interactions  can  l)e 
reduced  to  mathematics.  Because  of  their  essential  simj>licity, 
the  mathematical  sciences  have  been  carrieil  to  great  com- 
parative perfection.  It  is  easier  to  weigh  an  invisible  planet 
than  to  measure  the  force  of  heredity  in  a  grain  of  corn.  The 
sciences  of  life  are  inexact  because  the  human  mind  can  never 


10  EVOLUTION  AND   ANIMAL  LIFE 

grasp  all  their  data.  The  combined  effort  of  all  men,  the  flower 
of  the  altruism  of  the  ages,  which  we  call  science,  has  made 
only  a  beginning  in  such  study. 

But,  however  incomplete  our  reaUzation  of  the  laws  of  life, 
we  may  be  sure  that  they  are  never  broken.  Each  law  is  the 
expression  of  the  best  possible  way  in  which  causes  and  results 
can  be  linked.  It  is  the  necessary  sequence  of  events,  therefore 
the  best  sequence,  if  we  may  imagine  for  a  moment  that  the 
human  words  "good"  and  "bad'^  are  applicable  to  world 
processes.  The  laws  of  nature  are  not  executors  of  human 
justice.  Each  has  its  own  operation  and  no  other.  Each 
represents  its  own  tendency  toward  cosmic  order.  A  law  in 
this  sense  cannot  be  ''broken.'^  "If  God  should  wink  at  a 
single  act  of  injustice,^'  says  the  Arab  proverb,  "the  whole 
universe  would  shrivel  up  like  a  cast-off  snake  skin." 

The  laws  of  nature  have  in  themselves  no  necessary  principle 
of  progress.  Their  functions,  each  and  all,  may  be  defined  as 
cosmic  order.  The  law  of  gravitation  brings  order  in  rest  or 
motion.  The  laws  of  chemical  affinity  bring  about  molecular 
stability.  Heredity  repeats  strength  or  weakness,  good  or  ill, 
with  like  indifference.  The  past  will  not  let  go  of  us;  we  cannot 
let  go  of  the  past.  The  law  of  mutual  help  brings  the  perpetua- 
tion of  weakness  as  well  as  the  strength  of  cooperation.  Even 
the  law  of  pity  is  pitiless,  and  the  law  of  mercy  merciless.  The 
nerves  carry  sensations  of  pleasure  or  pain,  themselves  as  indif- 
ferent as  the  telegraph  wire,  which  is  man's  invention  to  serve 
similar  purposes.  Some  men  who  call  themselves  pessimists 
because  they  cannot  read  good  into  the  operations  of  nature 
forget  that  they  cannot  read  evil.  In  morals  the  law  of  compe- 
tition no  more  justifies  personal,  official,  or  national  selfishness 
or  brutality  than  the  law  of  gravitation  justifies  the  shooting 
of  a  bird. 

The  science  of  bionomics  centers  about  the  theory  of  descent, 
the  beUef  that  organs  and  species  as  we  know  them  are  derived 
from  other  and  often  simpler  forms  by  processes  of  divergence 
and  adaptation.  According  to  this  theory  all  forms  of  life 
now  existing,  or  that  have  existed  on  the  earth,  have  risen  from 
other  forms  of  life  which  have  previously  lived  in  turn.  All 
characters  and  attributes  of  species  and  groups  have  developed 
with  changing  conditions  of  Hfe.  The  homologies  among 
animals  are  the  results  of  common  descent.     The  differences 


EVOLUTION   DEFINED  H 

are  due  to  various  influences,  one  of  the  leading  forces  among 
these  being  competition  in  the  struggle  for  existence  between 
individuals  and  between  species,  whereby  those  best  adapted 
to  their  surroundings  live  and  rejiroduce  their  kind. 

This  theory  is  now  the  central  axis  of  all  biological  investi- 
gation in  all  its  branches,  from  ethics  to  histology,  from  anthro- 
pology to  bacteriology.  In  the  light  of  tliis  tlieory  every 
peculiarity  of  structure,  every  character  or  (juality  of  individual 
or  species,  has  a  meaning  and  a  cause.  It  is  the  v.ork  of  the 
investigator  to  find  tliis  meaning  as  well  as  to  record  the  fact. 
''One  of  the  noblest  lessons  left  to  the  world  by  Darwin,"  says 
Frank  Cramer,  "is  this,  which  to  him  amounted  to  a  profound, 
almost  religious  conviction,  that  every  fact  in  nature,  no  matter 
how  insignificant,  every  stripe  of  color,  every  tint  of  flowers, 
the  length  of  an  orchid's  nectary,  unusual  height  in  a  jjlant,  all 
the  infinite  variety  of  apparently  insignificant  things,  is  full  of 
significance.  For  him  it  was  an  historical  record,  the  revelation 
of  a  cause,  the  lurking  place  of  a  principle."  It  is  therefore  a 
fundamental  principle  of  the  science  of  bionomics  that  every 
structure  and  every  function  of  to-day  finds  its  meaning  in  some 
condition  or  in  some  event  of  the  past. 


CHAPTER  II 


VARIETY   AND   UNITY   IN    LIFh 


"L'especc,  c'est  iin  etre  qui  dans  ses  generations  successives 
presente  toujours  les  memes  caracteres  d 'organisation;  il  faut  ajouter 
dans  les  memes  localites,  et  les  memes  circonstances  exteriem-es. " — 
Rambur,  1842. 

"That  mystery  of  mysteries  as  it  has  been  called  by  one  of 
our  greatest  philosophers  " — this  is  Darwin's  phrase  regarding 

the  problem  before  us,  the 
origin  of  species — the  origin 
or  cause  of  variety  in  the 
life  of  the  globe. 

That  variety  exists,  that 
there  are  many  kinds  and 
types,  grades  and  grada 
tions  in  animal  and  vege- 
table life  is  evident  to  all. 
Birds  and  trees,  beetles 
and  butterflies,  fishes  and 
flowers,  ferns  and  blades  of 
grass,  all  these  are  objects 
of  constant  recognition. 
The  green  cloak  which 
covers  the  brown  earth  is 
the  shield  under  which 
myriads  of  organisms, 
brown  and  green,  carry  on 
their  life  work,  and  still 
farther  below  the  level  of 
our  ordinary  notice  exists 
a  range  of  hfe  scarcely  less 


Fig.  1. — Long-horned  boring  beetle  from 
Central  America  (one-half  natural  size).i 


^This  figure  and  the  others  in  this  chapter  are  introduced  simply  to 
Illustrate  graphically  the  variety  of  animal  form. 


12 


VARIETY  Av^  Ttxity   jx    iji.i.: 

varied.  Pasteur  has  defined  fermentation  as  ''life  witljouL  air.  ' 
A  liost  of  clieniical  changes  in  organic  matter,  fennentatioii, 
putrefaction,  infection  of  disease — all  these  are  the  work  of 
minute  organisms  none  the  less  real  because  invisible  and  im 
-;aried  in  form  and  structure  as  in  the  differing  cfTects  tiieir 
presence  may  produce. 

Each  kind  of  animal  or  plant,  that  is,  each  set  of  forms 
which  in  the  changes  of  the  ages  has  diverged  tangibly  from  its 
neighbors,  is  called  a  species.  There  is  no  absolute  definition 
for  the  word  species.  The  word  kind  represents  it  exact  1\-  in 
common  language,  and  is  just  as  susceptible  to  exact  definition. 


f 


'♦*^_. 


I****-*-' 


Fig.  2. — Kangaroo  rat  from  the  California-Mojave  desert  (one-half  natural  ^uc). 


The  scientific  idea  of  species  does  not  differ  materially  from  the 
popular  notion.  A  kind  of  tree  or  bird  or  squirrel  is  a  species. 
Those  individuals  which  agree  very  closely  in  structure  antl 
function  belong  to  the  same  species.  There  is  no  absolute  test, 
other  than  the  common  judgment  of  men  competent  to  decide. 
Naturalists  recognize  certain  formal  rules  as  assisting  in  such  a 
decision.  A  series  of  fully  intergrading  forms,  however  varie<l 
at  the  extremes,  is  usually  regarded  as  fornung  a  single  species. 
There  are  certain  recognized  effects  of  climate,  of  climatic  iso- 
lation, and  of  the  isolation  of  domestication.  These  do  not 
usually  make  it  necessary  to  regard  as  distinct  species  the 
extreme  forms  of  a  series  concerned. 

In  the  words  of  the  entomologist  Rambur,  "A  si)eeies  is  a 
group  of  beings  which  in  successive  generations  show  the  san^e 
characters  of  organization,  unchanged  so  lt)ng  as  the  locality 
and  external  conditions  icmain  unchanged." 


14 


EVOLUTION  AND  ANIMAL  LIFE 


The  number  of  species  actually  existing  is  far  beyond  ordi- 
nary conception.  The  earliest  serious  attempt  to  catalogue  the 
species  of  animals  and  plants  was  made  by  Linnaeus.  In  the 
tenth  edition  of  his  ''  Systema  Nature  ^'  in  1758,  in  the  823  pages 


Fig.  3. — Brittle  or  serpent  stars — species  undetermined.     (Natural  size,) 


devoted  to  animals,  he  describes  and  names  some  four  thousand 
different  kinds.  Great  as  this  number  seemed,  Linnaeus  ven- 
tured to  suggest  that  probably  his  pages  did  not  include  half  of 
those  kinds  of  animals  actually  existing. 

To-day  our  records  contain  descriptions  of  more  than  one 
hundred  and  fifty  times  as  many  kinds  of  animals  as  were  known 
to  Linnaeus  and  all  his  predecessors  and  all  his  associates  of  a 
century  and  a  half  ago.  Each  year,  since  1864,  there  has  been 
published  in  London  a  volume  called  the  "Zoological  Record.'^ 
Each  of  the  volumes — larger  than  the  whole  "  Systema  Naturae" 
■ — contains  the  names  of  the  animals  new  to  science  which  have 
been  added  to  the  system  in  the  year  of  which  it  treats.     In  the 


VARIETY   AND  UNITY   IX   LIFE 


1") 


record  of  each  year  we  find  aljout  twelve  tliousand  species,  about 
three  times  as  many  animals  as  in  the  whole  "  Systoina  Natura*." 
Yet  the  field  shows  no  signs  of  exliau.stion.  As  the  vohiiiics  of 
the  "Zoological  Record''  stand  on  tlie  shelves,  it  is  easy  to  see 
that  the  later  volumes  are  the  tliickest;  and  tliose  of  the  new 
century,  with  a  general  revival  of  interest  in  systematic  zoology 


Fig.  4. — California  quail,  Lopiionyx  californicus.     (Two-tliirds  natur.-il  ,si/,i-.> 


and  the  stud}^  of  geographical  distrihulion.  -avo  \]\c  tlii<'k('si  of 
all.  The  depths  of  the  S27,,  the  jungles  of  the  t ropier,  the  crev- 
ices of  the  coral  reefs,  the  tundras  of  the  north,  the  limhs  of 


16 


EVOLUTION  AND  ANIMAL   LIFE 


trees,  the  hair  of  mammals,  the  feathers  of  birds,  the  body 
tissues  of  mosquitoes,  all  places  where  animal  life  is  found,  are 
being  examined  with  an  eagerness  not  less  than  that  of  the  early 
explorers,  while  the  investigators  of  to-day  are  armed  with 
every  appliance  that  science  can  devise.  Yet  now,  as  in  Lin- 
nseus's  time,  it  is  certain  that  not  half  of  the  number  of  species 
of  animal  organisms  is  yet  known.     The  600,000,  more  or  less. 


Fig.  5. — Diamond  rattlesnake,  Crotalus  adamanteus.     (Photograph  by  W.  H.  Fisher.) 


on  our  registers  to-da}'  are  certainly  far  less  than  half  of  the 
millions  which  actually  exist. 

In  botany  we  find  the  same  conditions.  There  are  fewer 
known  species  of  plants  than  animals  by  half,  and  they  are  more 
easily  preserved  and  handled,  while  the  work  of  collection  and 
investigation  proceeds  on  a  scale  even  more  extensive,  yet  it 
would  be  a  bold  statement  to  say  that  we  know  to-day  half  the 
species  of  plants  that  exist. 

All  this  refers  to  the  forms  now  living,  without  reference  to 
the  host  which  composes  their  long  ancestry,  extending  back- 
ward toward  the  dawn  of  creation.  The  species  have  come 
down  through  the  geological  ages,  changing  in  form  and  func- 
tion to  meet  the  varying  needs  of  changing  environment.     This 


VARIETY   AND   UNITY   IN    LIFE 


1" 


enumeration  takes  no  account  of  tlio  still  vaster  myriads  of  forms 
almost  endlessly  varied  which  have  i)erished  utterly  in  the 
pressure  of  environment,  leaving  no  trace  in  the  line  of  descent. 


a 

U 

o 


L 


Of  these  extinct  forms  of  animals  and  plants  we  know  a  few. 
one  here  and  another  there;  here  a  bone,  there  a  tooth,  here  a 


18 


EVOLUTION   AND   ANIMAL   LIFE 


mass  of  shells,  there  a  piece  of  petrified  wood,  an  insect  in  the 
marl  bed  or  a  leaf  preserved  flat  in  the  shale.  Each  of  these 
fossils  is  a  record  of  past  life,  true  beyond  impeachment,  but 
the  fragments  are  so  few,  so  scattered,  so  broken,  as  to  give 
only  hints  of  the  history  they  represent. 

Moreover,  as  we  extend  our  studies  of  species  we  find  that 
they  change  with  space  as  well  as  with  time.     These  changes 


Fig.  7. — Common  lizard  or  swift,  Sceloporus  undulatus.     (Photograph  by  W.  H.  Fisher.) 


are  in  large  degree  a  response  to  external  conditions.  As 
conditions  change,  so  do  forms  change  to  fit  their  surroundings. 
A  movement  over  the  surface  of  the  earth,  any  movement  in 
space,  brings  organisms  in  contact  with  barriers.  A  barrier 
means  a  change  in  conditions  of  life.  As  distance  in  space 
brings  barriers,  so  does  the  passage  of  time  bring  events  which 
are  barriers  also,  Time  brings. new  events;  events  mean 
changes  in  conditions,  and  change  brings  about  divergence. 
Neither  time  nor  space  flows  evenly. 

Variations  in  turn  ^become  greater  with  lapse-  of  time  and 


VARIE1'\    A\D  UNITY  IX   LIFE 


10 


space,  for  these  again  bring  other  events  and  disclose  otlicr 
barriers.  A  closer  observation  will  show  us  that  the  range  of 
variety  is  far  greater  than  is  indicated  by  the  nunil)or  of  species. 
There  is  not  one  blade  of  grass  in  the  meadow  exactly  like  anv 
other  blade.  There  is  not  a  scpiirrel  in  the  forest  like  anv 
other  squirrel,  not  a  duck  on  the  ])oiid  like  any  other  duck  in 
every  detail  of  its  structure.  If  we  compare  two  rose  leaves 
we  shall  find  differences  in  size,  in  serration  of  the  margin,  in 
the  length  of  the  stalk,  in  the  hairs 
on  the  surface,  in  the  intensit}'  of 
the  green,  in  the  number  of  breath- 
ing pores  on  the  low^er  side.  In 
every  structure  and  function  where 
difference  is  i:)ossible  variation  will 
appear.  The  squirrels  or  the  ducks 
will  differ  in  shade  of  color,  in  dis- 
tinctness of  marking,  in  length  of 
limb,  in  breadth  of  organ,  in  every 
way  in  which  there  is  play  for  in- 
dividualism. 

Nor  are  these  differences  limited 
to  matters  of  color  or  form.  There 
are  like  variations  in  function,  in 
tendency,  in  disposition,  in  endur- 
ance. No  tw^o  men  ever  bore  the 
same  features,  no  two  ever  held  the 
same  character,  no  two  ever  lived 
the  same  life.  The  traits  of  the  in- 
dividual, however  small,  appear  on 
every  hand.     It  is  b}^  little  traits  of 

emphasis  that  we  recognize  our  friends.  The  same  individu- 
alism is  possessed  by  the  lower  animals  and  by  ])lants,  though 
the  differences  in  stress  and  emphasis  in  color  and  figure  are 
most  marked  in  creatures  of  the  most  highly  sj)ecialized  organi- 
zation. In  all  animals  and  all  plants  like  difTerences  obtain. 
No  two  individuals  of  any  species  are  ever  (juite  the  same.  No 
two  germ  cells  of  the  same  parent  are  ever  (juite  alikiv  Xo  two 
cells  in  the  body  are  ever  exactly  identical.  Among  |>lants  of 
the  same  kind  in  the  field,  some  are  cut  down  by  frost  while 
others  persist;  some  are  destroyed  by  drought  while  others  en- 
dure; some  are  immune  to  attacks  of  rust  while  others  arc  e.v 


FiG.    8. — Sea    cucumhfr.    Curu- 
ynaria,  sp.     (Natural  site.) 


20 


EVOLUTION  AND  AN'IMAL  LIFE 


TrG.  9.- -Blunt-nosed  salamander,  Amhlystoma  opacum.     (Photograph  by  W.  H.  Fisher.) 


Fig.  10. — White  pelicans,  Pelecanus  erythrorhynchus,  and  whooping-crane,  Grus  ameri- 

cana.     (Photograph  by  W.  H.  Fisher.) 


VARIETY  AND  rXlTY   IX   LIFE 


21 


terminated  by  such  parasites.  Fill  a  bottle  with  flies.  All  in 
time  will  die  of  suffocation,  but  a  certain  few  will  outlast  tlie 
msmy.  Bring  in  a  number  of  wolf  cubs.  Some  will  become 
relatively  tame — some  will  remain  wolves,  and  Ijetweeii  the 
most  fierce  and  the  most  docile  we  shall  find  all  ranges  of 
variation.  "What  is  one  man's  food  is  another  man's  poison." 
This  proverb  is  a  recognition  of  the  principle  of  individiudity 
which  accompanies  everywhere  the  formation  of  species,  and 
being  everywhere  present,  it  must  be  an  integral  i)art  of  the 


Fig.  11. — Silver  fox,  Vulpes  pennsylvanicua  argentatua.     (Photograph 

by  W.  H.  Fislier.) 


process.  Such  differences  are  not  matters  of  structure  alone. 
Psychological  differences,  differences  in  instinct,  in  adapta- 
bility, in  rate  of  nerve  processes  are  just  as  markjul  as  differ- 
ences in  anatomy.  They  may  separate  one  sj)ecies  fronj  an- 
other. They  may  be  just  as  decided  within  tlie  limits  of  the 
species  itself.  Moreover,  the  beginning  of  variation  is  not  with 
the  individual  organisms.  No  tw^o  cells  are  absolutely  alike, 
and  in  the  variance  of  the  germ  cells,  from  which  ii'.dividuals 
spring,  all  the  elements  of  their  future  variation  are  involved. 
Without  further  discussion,  it  is  evident  that  variety  in  life 
is  a  factor  in  the  history  of  our  globe,  that  it  may  be  exi)re.<.'ied 
in  terms  of  number  of  species,  but  that  the  actual  range  of  varia- 
tion is  far  greater  than  the  numl)er  of  s])ecies,  and  that  if  causes 
are  to  be  judged  by  range  of  effects,  we  must  find  in  the  origin  of 


EVOLUTION  AND  ANIMAL  LIFE 


species  the  operation  of  world-wide  forces,  the  cooperation  of 
great  influences,  far-reaching  in  time  and  space,  as  broad  as  the 
surface  of  the  globe  and  as  enduring  as  its  Hfe.  To  consider 
these  causes  so  far  as  known  is  the  purpose  of  this  work.  Our 
problem  is  no  longer  the  "mystery  of  mysteries,^'  for  in  a  large 
way  by  the  work  of  Darwin  and  his  successors  the  influences 
promoting  variety  in  life  are  already  known.  We  know  many 
of  the  different  factors  which  produce  divergence  in  form  and 
adaptation  to  conditions.  But  the  relative  value  of  these 
factors  is  less  certain,  and  from  time  to  time  other  and  more 


Fig.  12. — Lizard  walking.     (After  Marey.) 


subtle  factors  are  brought  to  light,  or  the  great  forces  them- 
selves are  analyzed  into  finer  component  elements. 

But  with  all  that  we  may  say  of  the  universality  of  variation 
and  the  prevalence  of  individualism,  we  are  equally  impressed 
with  the  underlying  unity.  There  are  onl}^  a  few  types  of 
structure  among  animals,  and  in  these  few  the  beginnings  in 
development  are  the  same.  The  plants  show  similarly  a  few 
modes  of  development,  and  all  the  range  of  families  and  forms 
is  based  on  the  modification  of  a  few  simple  types.  Moreover 
all  living  forms,  plants  and  animals  alike,  agree  in  the  funda- 
mental elements.  All  are  made  of  a  framework  of  cells,  each 
cell  a  source  of  energy,  containing  in  all  cases  a  semifluid  net- 
work of  protoplasm,  which  is  found  wherever  the  phenomena 
of  life  appear.  In  all  the  cells  is  the  mysterious  nuclear  sub- 
stance which  seems  to  direct  the  operations  of  heredity.  The 
same  laws  or  methods  of  heredity,  variability,  and  response  to 


VARIETY   AND   UNITY   IN    LIFE 


2:^ 


outside  stimulus  hold  in  all  the  organic  world.  We  call  animals 
and  plants  "organic"  because  they  are  made  up  of  organs, 
cells,  and  tissues  so  grouped  that  like  structures  perform  like 
functions.  We  could  not  use 
a  generic  term  like  organic, 
were  it  not  for  the  structural 
resemblances  existing  in  each 
individual  in  great  groups  of 
organisms.  All  organisms 
have  the  impulse  to  repro- 
duction. All  are  forced  to 
make  concession  after  con- 
cession to  their  surroundings 
and  in  such  concessions  prog- 
ress in  life  consists.  At 
last  each  organism  or  each 
alliance  of  organisms  is  dis- 
solved by  the  process  of 
death. 

The  unity  in  life  is  then 
not  less  a  fact  than  the 
diversity.  However  great 
the  emphasis  we  lay  on  in- 
dividuality or  diversity,  the 
essential  unity  of  life  must 
not  be  forgotten.  Whatever 
solution  we  may  find  to  the 
prol^lem  of  the  origin  of 
species,  must  also  explain 
why  species  and  individuals 
may  be  so  much  alike  in  all 
large  details  of  structure. 
To  know  the  origin  of  species 
we  must  also  know  why 
species  admit  of  natural 
classification.  Why  is  variety 
in    life    based    on    essential 

unity? 

From  the  fundamental  unity  of  the  species  of  to-day.  \u' 
may  infer  the  similar  unity  of  species  in  past  time.  Trom  tlie 
knowledge  of  variety  in  unity  comes  the  likenimr  of  species  of 


Fig.    13.— Starfish   walking.     (.\ft<*r 
Marey.) 


24 


EVOLUTION   AND  ANIMAL  LIFE 


animals  or  plants  to  the  separated  twigs  of  a  tree,  of  which 
the  trunk  is  more  or  less  concealed.  "We  can  only  predicate 
and  define  species  at  all/'  says  Dr.  Elliott  Coues,  "from  the  mere 
circumstance  of  missing  links.  Oiu-  species  are  twigs  of  a  tree 
separated  from  the  parent  stem.  We  name  and  arrange  them 
arbitrarily,  in  default  of  a  means  of  reconstructing  the  whole 
tree,  in  accordance  with  nature's  ramifications.''     To  continue 


Fig.  14. — Heron  flying.     (After  Marey.) 

the  figure,  in  our  studies  of  the  origin  of  the  twigs  of  the  tree, 
the  existence  of  the  trunk  must  not  be  forgotten.  In  the  life 
of  the  earth  variety  in  unity,  unity  in  variety  are  nowhere 
separated. 

Another  equally  striking  simile  is  this:  A  species  is  an 
island,  a  genus,  an  archipelago,  in  a  sea  of  death.  The  species 
is  clearly  definable  only  as  its  ancestors  and  cousins  have  dis- 
appeared, only  in  the  degree  that  the  stages  in  its  develoi3ment 
are  unrepresented  in  our  records.  The  genus  is  a  group  of 
species,  an  archipelago  of  islands,  and  there  may  be  every 
conceivable  degree  of  width  or  breadth  of  channel  which  seems 
to  separate  one  island  or  group  of  islands  from  another. 


j:>r^'. 


/ 


CHAPTER  III 

LIFE,   ITS  PHYSICAL  BASIS  AND    SIMPLEST 

EXPRESSION 

There  can  be  little  doubt  that  the  further  science  advances  the 
more  extensively  and  consistently  will  the  phenomena  of  nature  be 
represented  by  mathematical  formula  and  symbols.  But  the  man  of 
science  who,  forgetting  the  hmits  of  philosophical  inquiry,  sliiles  from 
these  formulae  and  symbols  into  what  is  commonly  understood  by 
materiaUsm,  seems  to  me  to  place  himself  on  a  level  with  the  mathe- 
matician who  should  mistake  the  x's  and  y's  \\'ith  which  lie  works  his 
problems  for  real  entities,  and  with  this  further  disadvantage  as 
compared  with  the  mathematician,  that  the  blunders  of  the  hitter 
are  of  no  practical  consequence,  while  the  errors  of  systematic  materi- 
alism may  paralyze  the  energies  and  destroy  the  beauty  of  a  hfe. — 
Huxley. 

In  practice  the  distinction  between  a  live  thing  and  a  lifeless 
one  is  usually  of  the  simplest,  but  to  define  this  distinction  in 
terms  so  precise  that  the  definition  may  be  used  as  an  invariable 
criterion  is  a  problem  of  considerable  difliculty.  Tlie  sheep 
grazing  in  the  field  and  the  soil  under  its  feet;  the  grass  and 
flowers  on  the  one  hand,  and  the  stones  on  the  other  hand,  in 
the  same  pasture;  there  are  no  dilliculties  in  tlie  distinction 
here.  Nor,  indeed,  even  when  we  come  to  considtM'  tlie  siinpU^st 
kinds  of  organisms,  the  tiny  one-celled  i)lants  and  animals  that 
teem  in  stagnant  w'aters  of  the  wayside  puddle.  As  we  examine 
a  drop  of  this  water  under  the  microscope  wc  know  without 
question  what  in  it  is  alive  and  what  in  it  is  dead. 

But  let  us  attempt  to  put  into  words,  into  (h^fiiiite  declaratory 
phrases,  the  characteristics  of  organisms  and  wt'  iiiul  ourselves 
curiously  impotent.  When  we  come  to  study  analytically 
organic    nature    and    inorganic    nature,    things    animate   and 

23 


26  EVOLUTION  AND  ANIMAL  LIFE 

things  inanimate,  we  find  structures  and  behavior  among  inor- 
ganic things  which  cannot  be  readily  distinguished  in  defining 
words  from  structures  and  behavior  that  are  usually  taken  as 
characteristic  of  organisms.  On  the  other  hand  we  shall  find  in 
organic  nature  the  very  same  chemical  elements,  and  for  the 
most  part  the  same  combinations  of  elements,  th^t  we  find  in 
the  great  mass  of  inorganic  world  substance.  So  that  some 
biologists  by  a  detailed  and  keen,  if  somewhat  sophisticated, 
analysis  of  the  alleged  differences  between  animate  and  inani- 
mate matter  show  that  these  differences  are  not  absolute,  and 
leave  you  with  a  stone  in  one  hand  and  a  grasshopper  in  the 
other  logically  unable  to  define  the  fundamental  difference 
between  the  tAvo,  and  yet  morally  certain  of  this  absolute 
difference. 

As  a  matter  of  fact  there  is  one  distinction  between  living 
matter  and  non-living  matter  which  even  the  cleverest  of  the 
modern  physicochemical  school  of  biologists  has  as  yet  been 
unable  to  explain  away.  And  that  is  the  inevitable  presence  in 
living  matter  and  the  inevitable  absence  in  non-living  matter 
of  certain  highly  complex  chemical  combinations  of  carbon, 
hydrogen,  oxygen,  nitrogen,  and  sulphur,  called  proteids  or 
albuminous  compounds. 

The  actual  presence  of  these  chemical  substances  in  living 
matter  is  made  manifest  to  us  by  the  physicochemical  behavior 
of  these  substances:  that  is,  by  our  observation  or  recognition 
of  their  peculiar  attributes.  This  behavior  or  these  peculiar 
attributes  or  activities  are  those  fascinating  ones  which  we  are 
accustomed  to  call  the  essential  life  processes.  What  these 
activities  are  we  indicate  in  a  not  very  precise  way  by  the 
words  organization,  assimilation,  growth,  reproduction,  motion, 
irritability,  and  adaptation.  These  essential  life  processes  we 
have  come  by  constant  experience  to  associate  always  and  only 
wdth  a  substance  called  protoplasm.  Huxley  long  ago  called 
protoplasm,  therefore,  the  physical  basis  of  life. 

But  protoplasm  we  have  found  to  be  a  complex  of  substances 
or  chemical  compounds.  Of  these,  a  certain  few  are  indispen- 
sable and  fundamental,  while  others  may  be  absent  or  present 
without  affecting  the  particular  capacities  which  make  proto- 
plasm the  physical  basis  of  life.  This  protoplasm  too  must  be 
organized  in  a  particular  way  in  order  that  Ufe  m^ay  persist  in 
the  organism.     It  must  appear  in  two  conditions,  and  proto- 


LIFE,  ITS   PHYSICAL .  BASIS   AND  SIMPLEST   EXPHi:SSIO\   27 

plasmic  stuff  representing  these  two  conditions  must  !)e  disposed 
in  certain  definite  relations.  Protoplasm  nuist  occur  as  a  cell 
or  cells  to  be  capable  of  performing  the  necessary  activities  of 
life.  Hence  we  must  consider  at  the  very  begimiing  of  any  dis- 
cussion of  life  the  two  things,  protoplasm  and  the  cell. 

The  elements  tiiat  compose  protoplasm  are  the  familiar  ones, 
carbon,  nitrogen,  h3Tlrogen,  oxygen,  sulphur,  phosphorus, 
potassium,  sodium,  etc.;  but  these  elements,  or  some  of  them, 
are  found  in  protoplasmic  cells  in  certain  comj)lex  combiiialion.s 
which  arc  not  found  elsewhere  in  nature,  and  which  thcrcfon! 
actually  and  absolutely  distinguish  chemically  living  proto- 
plasm from  all  lifeless  matter.  These  particular  com))inations 
are  certain  albuminous  compounds  or  proteids,  comj)os('d  of 
C,  H,  O,  N,  and  S,  and  their  complexity  is  extreme:  the  atoms 
in  a  single  molecule  often  number  more  than  a  thousand.  The 
molecules  also  are  very  large,  which  is  proljably  the  reason  of 
their  characteristic  nondiffusibility  through  animal  membranes 
or  artificial  parchment. 

In  addition  to  these  characteristic  all)uminous  compounds 
and  various  derivatives  of  them,  proto])lasm  usual' y  contains 
certain  native  albumins  and  certain  other  characteristic  com- 
pounds known  as  carbohydrates  and  fats  (wliich  differ  essen- 
tially from  the  albuminous  substances  in  lacking  nitrogen  as  a 
composing  element).  There  are  also  various  salts  and  gases 
and  alwavs  water  to  be  found  in  Uving  substances,  ^^'ate^  is 
absolutely  necessary  to  the  physical  condition  of  half  fluidity 
which  gives  to  protoplasm  its  essential  capacity  for  motion  on 
itfc^lf.  The  commoner  salts  found  in  hving  substances  are 
compounds  of  chlorine  as  well  as  the  carbonates,  suli)hates,  and 
phosphates  of  the  alkalies  and  alkali  earths,  especially  conunon 
salt  (sodium  chloride),  potassium  chloride,  annnoniiun  chh^nde, 
and  the  carbonates,  sulphides,  and  suli)hates  of  sodium,  jwtjis- 
sium,  magnesium,  ammonium,  and  calcium.  The  gases  found 
in  Uving  matter  are  oxygen  and  car])on  dioxide.  Tlics'  .  when 
not  in  chemical  combination,  are  almost  always  dissolved  in 
water,  although  rarely  they  may  be  in  the  Umn  of  gas  hubblrs. 

To  sum  up  the  relation  of  living  matter  to  chemistry  we  may 
say  that  life  is  always  associated  with  jirotoplasm.  and  that  this 
protoplasm  is  made  up  of  a  few  familiar  inorganic  elements, 
particularly  those  of  lowest  atomic  weight;  that  it  does  not 
include  any  special  so-called  vital  or  life  element,  that  is.  any 


28  EVOLUTION   AND  ANIIVIAL   LIFE 

elementary  substance  other  than  occurs  in  the  inorganic  world. 
These  elements  are  combined  in  protoplasm  into  certain  most 
extremely  complex  compounds^  which  are  always  present  where 
life  is,  and  never  elsewhere^  and  hence  the  essential  chemical 
characteristic  of  living  matter  is  the  presence  of  these  complex 
as  yet  unanalyzed,  albuminous  compounds. 

It  is  obvious  that  this  chemical  half-knowledge  of  proto- 
plasm makes  no  satisfying  revelation  to  us  explanatory  of  the 
qualities  of  this  life  stuff.  How  is  it  then  with  the  physical 
structure  of  protoplasm?  We  know  that  many  simple  chemical 
substances  put  together  in  particular  physical  relationship  to 
each  other  will  give  a  capacity  of  performance  or  function  quite 
different  from  and  beyond  that  which  they  possess  when  simply 
brought  together  without  definite  order  or  arrangement.  Is 
protoplasm  a  machine  with  a  capacity  for  doing  extraordi- 
nary things,  with  its  powers  due  primarily  to  its  physical 
make-up?  Unfortunately  weliave  no  satisfying  answer  to  this 
question.  While  chemists  are  balked  in  their  analysis  of  the 
protoplasmic  make-up  by  the  complexity  of  the  compounds 
they  meet;  a  complexity  too  much  for  their  present  technic  to 
resolve,  physicists  are  similarly  balked  in  their  attempt  to  re- 
solve and  expose  the  ultimate  physical  structure  of  protoplasm. 

This  ultimate  structure  of  protoplasm  is  ultramicroscopic, 
and  its  study  is  checked  by  the  limitations  of  microscopes. 
When  we  examine  protoplasm  with  the  highest  powers  of  the 
microscope  we  see  plainly  that  it  is  not  as  it  appears  under  lower 
powers,  structureless  and  homogeneous.  On  the  contrary  it 
reveals  an  apparent  granular  or  fibrillar  or  alveolar  or  reticu- 
lar structure.  We  find  that  protoplasm  varies  in  its  physical 
make-up  at  different  times  or  in  different  cells.  We  also  find 
that  the  difficulties  of  interpreting  just  what  one  sees  when  using 
the  highest  microscopic  powers  make  it  impossible  to  be  really 
certain  of  understanding  what  is  seen.  But  however  various 
our  interpretations  of  the  finer  structure  of  protoplasm,  they 
agree  that  any  bit  of  protoplasm  is  a  viscous  colloidal  mass 
composed  of  at  least  two  substances  of  somewhat  different  phys- 
ical make-up.  One  of  these  substances  is  evidently  denser  than 
the  other  and  is  arranged  in  the  form  of  grains,  rods,  threads, 
or  droplets  scattered  through  a  ground  mass.  Concerning  this 
dimorphic  condition  of  protoplasm  practically  all  biologists  are 
agreed.    The  names,  hyaloplasm,  paraplasm,  or  others  of  sim- 


LIFE,  ITS  PHYSICAL  BASIS  AND  SIMPLEST   EXPRESSION'  29 

ilar  significance  are  applied  to  the  viscous  livaline  -mun.I 
substance,  while  the  denser  parts  are  variously  called  "inicro- 
somes,  granules,  fibrils,  sponfj;ioplasni,  etc. 

The  important  part  of  all  this  is  the  fact  that  all  the  biclo^rims 
are  not  agreed  on  any  certain  kind  of  iniiinate  structure  of 


Fig.  15. — Different  types  of  cells  composing  the  body  of  the  .«quirrel  or  other  hichly 
developed  animal:  A,  liver  cell;  /,  food  nialerials;  «,  nucleus;  li.  complete  chII; 
C,  nerve  cell,  with  small  part  of  its  fiber;  D,  nmsrle  fiber;  K,  cells  luiiiie  ihf  J..h!v 
cavity;  F,  lining  of  the  windpipe;  G,  section  through  the  skin.     (Highly  niut: 

protoplasm  as  revealed  by  the  highest  powers  of  the  inicroscoj)o, 
but  they  all  agree  that  there  is  a  fine  and  real  structural  orj^aii- 
ization  of  what  at  first  glance  a])pears  to  be  honiogcuoous 
structureless  life  stuff.  That  is,  as  Delage  expresses  it,  it  is  seen 
that  protoplasm  is  not  simply  an  organic  chemical  compound. 
but  that  it  is  an  organized  substance;  that  is,  it  po.--;- 
structure  of  a  higher  order  than  tlie  automatic  struct iwe  of  tlio-'" 
chemical  molecules  which  compose  non-living  so-called  organir 
substances.     But  at  the  same  time  we  arc  deceived  if  we  exiH'ct 


30 


EVOLUTION  AND  ANBIAL  LIFE 


to  be  able  to  find  in  this  physical  organization  of  protoplasm 
any  satisfactory  explanation  of  its  wonderful  properties. 

We  have  said  that  it  should  always  be  held  clearly  in  mind 
that  the  full  life  capacity  of  protoplasm  is  reahzed  only  when  it 
is  in  that  differentiated  and  organized  condition  typical  of  the 
structural  unit  or  cell.  The  essential  thing  about  the  cell  is 
not  that  it  has  a  definite  shape  or  size  or  that  it  is  truly  cell-  or 
sachke,  but  that  it  is  a  tiny  mass  of  protoplasm  with  various 


■',«"5r:  -^^  / 


^i>J 


Fig.   16. — ^Amceba,  showing  different  shapes  assumed  by   it  when  crawHng.     (After 

Verworn.) 


substances  secreted  by  or  held  in  it.  The  protoplasm  itself  is 
differentiated  into  at  least  two  parts,  an  inner,  denser,  smaller 
part  called  the  nucleus,  and  an  outer  surrounding,  usually  larger, 
portion  called  the  cytoplasm.  Such  a  differentiated  or  organized 
protoplasmic  unit  can  perform  all  of  the  essential  functions  of  hfe 
and  persist  in  tliis  performance  indefinitely  unless  destroj^ed  by 
extrinsic  causes.  The  cell  itself  may  not  have  any  indefinite 
existence  as  a  unit,  but  it  will  be  the  progenitor  of  an  indefi- 
nitely prolonged  series  of  cells.  A  single  part  of  this  cell,  that  is, 
a  bit  of  protoplasm  either  of  the  nucleus  or  the  cj^toplasm,  or  the 
whole  of  either  can  perform  for  a  while  most  of  the  activities  of 
life;  but  such  a  part  always  lacks  the  capacity  for  reproduction, 
that  iS;  for  persistence  as  hving  matter.     Thus  it  is  obvious  that 


LIFE,  irs  PHYSICAL  BASIS  AND  SLMPLE.sT  EXPUESSIOX     .31 


Fig.  17.— Amoeba  eating  a  microscopic  one-celled  plant.     (Afi«T  Vcrworn.) 


Fig.  18. — Amceho  pnli/podin  in  six  succes.sive  stajtes  of  Cssion.     TJu«  tl;it  k  m  iii(c^iimrKiii<Hl 
spot  in  tiie  interior  is  the  micleiis.      (  Vfu-r  I".  I!.  S<'h»»Il»«".) 


S2 


EVOLUTION  AND  ANIMAL  LliB^E 


if  such  protoplasmic  cells,  composed  of  nucleus  and  cytoplasm, 
exist  singly  they  form  living  units.  And  we  have  actual  ex- 
emplifications of  this  condition  in  the  structure  and  life  of  the 
simplest  organism. 

The  simplest  organisms  are  independently  living,  single  proto- 
plasmic cells  (Figs.  16-21).     There  are  thousands  of  kinds  of 


Fig.  19. — Plasmodium  of  a  slime  mold  on  wood,  Trichia  favaginea:  A,  Plasmodium  X  2; 
B,  spores;  C,  spore  with  contents  escaping;  D,  ciliated  swarm  spore,  showing 
flagellum,  /,  and  nucleus,  n;  E,  two  ama?boid  swarm  spores;  F,  part  of  Plasmodium 
under  glass  slide;  G,  a  part  of  F,  more  highly  magnified.     (After  Campbell.) 


these  single-celled  organisms  recognizably  different  by  charac- 
teristics of  shape  and  size,  habit  and  habitat.  We  try  to  distin- 
guish them  as  single-celled  animals  (Protozoa)  and  single-celled 
plants  (Protophyta) ,  on  the  basis  of  alleged  differences  in  their 
habit  of  food-taking  and  general  nutrition.  This  distinction  is 
often  most  arbitrarily  made,  and  botanists  and  zoologists  are 
constantly  claiming  the  same  organisixis  as  belonging  to  their 
respective  fields  of  study.  Many  naturalists,  conspicuously 
Haeckel,  have  repeatedly  suggested  the  convenience  and  even 
the  necessit}^  of  grouping  most  of  these  unicellular  organisms 
into  a  phylum  or  kingdom  to  be  called  the  Protista,  the  members 


LIFE,  ITS   PHYSICiU.   BASIS   iVND  SIMPLKST   KXPIU-SSK  )\   .'^3 


of  which  shall  not  bo  recognized  as  siifTiciontly  specialized  (o  he 
called  either  plants  or  animals,  but  simply  organisins.  J^ut 
this  suggestion  seems  to  meet  with  little  practical  favdr  frnr,. 
students  of  systematic  biology. 

For  a  basis,  therefore,  of  any  study  of  the  evolufinn  f.f  lif.., 
an  acquaintanceship  with  the  life  and  struc- 
ture of  the  simplest  organisms  is  a  necessity. 
As  the  authors  have  already  tried  in  another 
book  ("Animal  Life")  to  present  a  simple 
account  of  this  hfe  together  with  an  account 
of  certain  less  simple  or  slightly  complex  or- 
ganisms (Figs.  22-26)  wliose  physiology  and 
structure  reveal  successive  stages  in  organic 
complexity  and  specialization,  and  as  tlie  spac(> 
in  this  book  is  Hmited,  the  authors  must 
refer  their  present  readers  to  chapters  I,  II, 
and  III  of  "Animal  Life  "  for  an  account 
of  the  life  of  the  simplest  and  sliglitly  com- 
plex organisms. 

The  differentiation  and  growing  com- 
plexity of  the  body  of  those  many-celled 
animals  wliich  differ  from  and  are,  we  mav 
say,  beyond  and  higher  than  the  simple  many- 
celled  forms,  are  by  no  means  always  along 
the  same  Une  (Figs.  27-37).  It  is  familiar 
knowledge  that  animals  can  be  classified  or 
grouped  into  a  number  of  great  divisions 
called  branches  or  phyla.  For  example,  the 
starfishes,  sea  urchins,  sea  cucumbers,  etc., 
constitute  one  phylum,  the  Echincdermata; 
the  crustaceans,  insects,  spiders,  etc.,  con- 
stitute another  phylum,  the  Arthropoda,  and 
all  the  animals  with  a  backbone  or  with  a 
notochord  constitute  another,  the  Chordata. 
of  these  phyla  there  is  a  fundamental  or  type  structure  (Fi_ 
27).  All  of  the  Echinodermata,  for  example,  arc  buih  on  the 
radiate  plan.  Tliey  recall  the  starfish  with  its  five  or  more 
arms  radiating  from  a  central  disk.  Tlie  Arthro]-)0(ls  are  all 
animals  with  a  bod}^  composed  fundamentally  of  a  series  of 
successive  segments,  some  or  all  of  these  segments  bearing 
pairs  of  jointed  appendages;  and  so  on.     We  need  not  pursue 


^jiir 


Tie. 


23.  —  Paranift- 
ciitm  aureliti.  At 
each  OIK  I  there  is 
a  contractile  vac- 
uole, ami  in  the 
con  tor  is  one  of 
(he  nuclei.  (After 
\'erworn.) 


Xow   for   each 


34 


EVOLUTION   AND  ANIMAL  LIFE 


Fig.  21. — A  group  of  stalked  one-celled 
animals,  Carchesmm.  sp.  (Adapted  from 
Davenport,  from  a  photograph  of  the  liv- 
ing animals.) 


grouped  into  two  regions  and 
the  appendages  limited  to 
the  anterior  one  of  these 
two.  The  Myriapods,  which 
are  also  Arthropods,  have  a 
structure  more  in  conformity 
with  what  may  be  called  the 
racial  or  typical  plan  for  the 
whole  phylum;  that  is,  the 
body  is  made  up  of  a  series 
of  many  successive  similar 
segments,  each  segment  bear- 
ing a  pair  of  jointed  ap- 
pendages. In  that  general 
line  of  descent  to  which 
man  belongs,  and  which  is 
distinguished  by  the  name 
of  the  phylum  Chordata, 
there  are  of  course  various 
subordinate  lines  which  we 
lecoguize   under   the   names 


further  the  general  classifi- 
cation of  animals  into  phy- 
la. Nor  need  we  explain 
in  any  detail  the  structural 
types  or  fundamental  struc- 
tural plans  which  distin- 
guish the  various  principrJ 
lines  of  descent  in  the 
animal  kingdom. 

Branching  out  from  each 
of  the  principal  lines  are 
hosts  of  subordinate  lines. 
Some  of  the  Arthropods,  r:s 
the  insects,  have  their  body 
segments  grouped  into  three 
regions  and  their  jointed 
appendages  confined  to  the 
anterior  two  of  these  re- 
gions. Others,  as  the  spide:  s, 
have     the     body    segments 


Fig.  22. — Gonium  pectorale,  a  colonial  pro- 
tozorin:  A,  seen  from  above;  B.geen  from 

the  side.    (After  SteiaO 


LIFE.  ITS  l^HYSICAL  BASIS   AXD  SIMPLEST  EXPniOSSIu.N   oO 


Fig.  23. — Pnndin-init  np.,  a  rolnnial 
pri>t(iZ(><ji».     UliKlily  iniiimifi(xj.) 


of     fishes,     amphibians,     reptiles, 
birds,  and  mammals. 

In  all  the  subdivisions  of  tiic 
main  groups  there  are  also  to  be 
recognized  differentiated  and  di- 
vergent lesser  lines  of  descent,  and 
within  these  still  lesser  ones. 
While,  as  already  noted,  the  main 
divisions  of  the  animal  kingdom 
are  called  phyla  and  the  divisions 
of  the  phyla,  classes,  the  subdi- 
visions of  the  classes  are  usually 
called  orders.  The  next  subdi- 
vision is  that  into  families,  each 
in  turn  being  a  cluster  of  genera. 

The  genera  are  composed  of  species  and  the  species  finuli\   ui 
sub-species,  varieties,   and   individuals.      I*^ach   one  of    tlu^sc 

names  refers  p;:- 
marily  to  a  spocial 
line  or  mode  of 
differentiation  and 
at  the  same  time 
refers  to  tlie  fact 
that  the  members 
of  each  of  tlie.><e 
(1  i  f  f  (^  r  ( '  n  t  i  a  t  e  cl 
groups  are  genet- 
ically related  to 
each  other.  t!i:it 
is,  related  l>y 
blood,  by  actu;'.l 
ancestral  descent. 
All  these  diffcr- 
enliated  groups 
indicate  diverging 
lines  of  cvolutinn. 
some  of  flieni 
short,    ami    but 

Fig.  24.— a  fresh-water  polyp,  Hiidm  vulgaris:   A.  in  ex-  sliglltly     diverg*'nt 

tended  condition  and  in  contraofod  condition;    H,  cross  from      tllC      MlJlih 

section  of  body,  showing  the   two  layers  of  cells  which  ..             from       Nvlucll 
make  up  the  body  wall. 


36 


EVOLUTION  AND  ANIMAL  LIFE 


they  arise;  others,  on  the  contrary,  long,  important,  and  widely 
divergent. 

The  traditional  tree  which  is  drawn  to  explain  animal 
classification  illustrates  at  the  same  time  the  two  fundamental 
facts  upon  which  this  classification  is 
based,  namely,  differentiation  of  struc- 
ture, and  corresponding  divergence  of 
descent.  All  the  branches  of  this  gene- 
alogical tree  lead  back,  as  they  do  in  a 
real  tree,  to  its  trunk,  and  the  trunk 
of  this  tree  springs  from  the  simplest  of 
the  many-celled  animals,  namely,  from 
those  primitive  form.s  which  resemble  in 
essential    characters    animals    like    the 


Fig.  25. — Longitudinal  section  through  the  body 
of  a  sea  anemone:  oe.,  cesophagus;  r«./.,  mesen- 
terial filaments;  r.,  reproductive  organs. 


Fig.  26. — One  of  the  sim- 
plest sponges,  Calcoljjn- 
ihus  primigenius.  A  part 
of  the  outer  wall  is  cut 
away  to  show  the  inside. 
(After  Haeckel.) 


simpler  polyps.  Indeed  it  seems  certain  that  this  tree  trunk 
can  be  traced  farther  back;  that  it  must  spring  in  the  begin- 
ning from  forms  essentially  like  the  lowest  organisms  that  w^e 
know  to-day,  namel}^,  single,  simple  cells  living  independently. 
From  the  Amoeba  to  Man;  that  is  the  history  of  descent,  or 
ascent  if  one  prefers.  The  course  has  been  a  continuous  one, 
both  in  point  of  time  and  in  point  of  gradual  transformation. 


LIFE,  ITS   PHYSICAL  B.4SIS   A.NU  SlMl-Ll^sL   L.M-,;,..ssi..,.N    .-(7 

/ 


Fig.  27. — Diagi-am  showing  fundamental  structure  of  types  of  several  nniinnt  ptiyiA: 
1,  sea  anemone;  2,  starfish;  3,  worm;  4.  centipe.le;  5.  clam;  0.  honeylnf;  7. 
mander.      In  ei  ch  figure  the  central  nervous  system  is  indicated  I'y  the  Mack  Im.  - 
(After  Haeckel.) 

t 

But  great  periods  of  tliis  time  (ire  shut  iiway  fioni  i;.s  wiiliout 
record  of  their  duration,  and  lon<^  series  of  the  i^radu.-dly 
changing  forms  are  lost  to  us  withor.t  I.ojU'  of  discovery.  And 
yet  in  its  large  outlines  we  know  the  liistory  of  all  this  time 
and  the  character  of  all  these  gratletl  series. 


38 


EVOLUTION   AND  ANIMAL  LIFE 


We  should  give  at  least  brief  attention  to  what  may  be  called 
the  primary,  or  necessary,  conditions  of  life.  We  know  that 
fishes  cannot  live  very  long  out  of  water  and  that  birds  cannot 
five  in  w\ater.  These,  however,  are  conditions  which  depend  on 
the  special  ecological  habits  of  these  two  particular  kinds  of 
animals.  The  necessity  of  a  constant  and  sufficient  supply  of 
oxygen  is  a  necessity  common  to  both.  It  is  one  of  the  primary 
conditions  of  their  life.  All  animals  must  have  air.  Similarly 
both  fishes  and  birds  and  all  other  animals  must  have  food. 

This,  then,  is  an- 
other of  the  pri- 
mary conditions  of 
animal  life. 

If  water  be  held 
not  to  be  included 
in  the  general  con- 
ception   of    food, 
then    special    men- 
tion must  be  made 
of  the  necessity  of 
water    as     one     of 
the  primary  condi- 
tions of  life.    Proto- 
plasm, the  basis  of  fife,  is  a  fluid,  although  thick  and  viscous. 
To  be  fluid  its  components  must  be  dissolved  or  suspended  in 
water.     In  fact,  all  of  the  really  living  substance  in  an  animal's 
body  contains  water.     This  water,  so  necessary  for  the  animal, 
may  be  derived  from  the  general  food,  all  of  which  contains 
water  in  greater  or  less  quantity,  or  it  may  be  taken  apart  from 
the  other  food  by  drinking  or  by  absorption  through  the  skin. 
We  know,  too,  that  if  the  temperature  is  below  a  certain 
minimum  point  or  above  a  certain  maximum,  these  points  vary- 
ing for  different  animals,  death  takes  the  place  of  life.     It  is 
familiar  knowledge  that  many  animals  can  be  frozen  without 
being  killed.     Insects  and  other  small  animals  may  fie  frozen 
through  winter  and  resume  active  life  again  in  the  spring.     An 
experimenter  kept  certain  fishes  frozen  in  blocks  of  ice  at  a  tem- 
perature of  —15°  C.  for  some  time  and  then  gradually  thawed 
them  out  unhurt.     There  is  no  doubt  that  every  part  of  the 
body,  all  of  the  living  substance,  of  these  fish  was  frozen,  for 
specimens  at  this  temperature  could  be  broken  ^nd  pounded  up 


Fig.  28. — The  fiddler  crab,  Gelasimus. 
Miss  Mary  Rathbun.) 


(Photograph  by 


LIFE,  ITS   PHYSICAL   BASIS   AND   SIMPLEST   EXPRESSION   39 

into  fine  icy  powder.  But  a  temperature  of  —20°  C.  killccl  the 
fisli.  According  to  L.  J.  Turner,  tlie  Alaska  nuid-fi.sli  (Dallia), 
was  fed  frozen  to  Esquimaux  dogs.  One  of  these  thawing  in 
tlie  stomach  of  the  animal  made  its  escape  alive.  Frogs  lived 
after  being  kept  at  a  temperature  of   —28°  C,  centii)etles,  at 


Fig.  29. — ^The  piddock,  Zirphosa  crisputa,  a  rock-boring  mollusk.     "(Natural  size,  from 

life.) 


a  temperature  of  —50°  C,  and  certain  snails  endured  a  temjiera- 
ture  of  —120°  C.  without  dying. 

At  the  other  extreme,  instances  are  known  of  animals  living 
in  water  (hot  springs  or  water  gradually  heated  with  the  organ- 
isms in  it)  of  a  temperature  as  high  as  50°  C.  Experiments  with 
Amoebse  show  that  these  simplest  animals  contract  and  cease 
active  motion  at  35°  C,  but  are  not  killed  until  a  temperature 
of  40°  to  50°  C.  is  reached. 

Variations  in  pressure  of  the  atmosphere  also  constitute 


40 


EVOLUTION   AND  ANIMAL  LIFE 


conditions  which  may  determine  the  existence  of  hfe.  The 
pressure  or  weight  of  the  atmosphere  on  the  smface  of  the 
earth  is  nearly  fifteen  pounds  on  each  square  inch.  This 
pressure  is  exerted  equally  in  all  directions  so  that  an  object  on 
the  earth^s  surface  sustains  a  pressure  on  each  square  inch  of 


Fig.  30. — Cephalopods.  Lower  figure,  the  devil-fish  or  octopus,  Octopus  punctatus. 
The  upper  figure  represents  the  squid,  Loligo  pealii,  swimming  backward  by 
driving  a  stream  of  water  through  the  small  tube  slightly  beneath  the  eyes.  (From 
life,  one-third  natural  size.) 


its  surface  of  fifteen  pounds.  That  is,  all  animals  liv'ng  on  the 
earth's  surface  or  near  it  live  under  this  pressure  and  under 
no  other  condition.  The  animals  that  live  in  water,  how^ever, 
sustain  a  much  greater  pressure,  this  pressure  increasing  with 
distance.  Certain  ocean  fishes  live  habitually  in  great  depths,  at 
from  two  to  nearly  five  miles,  Avhere  the  pressure  is  equivalent  to 
that  of  many  hundred  atmospheres.  If  these  fishes  are  brought 
to  the  surface  their  eyes  bulge  out,  their  scales  fall  off  because 
of  the  great  expanse  of  the  skin,  and  the  stomach  is  thrust 
wrong  side  out.     Indeed  the  body  itself  sometimes  bursts-     Oa 


Life,  its  thysical  basts  and  simplest  expression  41 

the  other  hand  if  an  aninlal  which  hves  normaUy  on  the  surface 
of  the  earth  is  taken  up  a  very  high  mountain  or  is  carried  up  in 
a  balloon  to  a  great  altitude  where  the  pressure  of  the  atmos- 
phere is  much  less  than  at  the  earth's  surface,  serious  conse- 
quences may  ensue,  and  if  too  high  an  altitude  is  reached,  death 
occurs. 

Some  animals  require  certain  organic  salts  or  compounds 
of  lime  to  form  bones  or  shells,  etc.  These  salts  may  be  re- 
garded as  necessary  articles  of  nutrition,  though  their  function 
is  not  that  of  ordinary  food.  These  are  peculiar  demands  of 
special  kinds  of  animals.  There  might  also  be  included  an:iong 
primar}^  life  conditions  such  necessities  as  the  light  and  lieat  of 
the  sun,  the  action  of  gravitation,  and  other  jDhysical  conditions 


Fig.  31. — Long-horned  boring  beetle,  Ergates  sp. — larva,  pupa  and  adult  insect. 


without  which  existence  of  life  of  any  kind  would  be  impossible 
on  this  earth. 

Finally  we  may  refer  briefly  to  tlio  "grand  prol)lem  "  of  tlic 
origin  of  life  itself.  Any  treatnirnt  of  this  question  is  bound  to 
be  wholly  theoretical.  We  do  not  know  a  single  positive  thing 
about  it.     We  have  some  negative  evidence.     Tliat  is,  we  liave 


42 


EVOLUTION   AXD   ANIMAL   LIF13 


no  recorded  instance— and  men  have  searched  dihgently  for 
examples— of  spontaneous  generation.  No  protoplasm  has 
been  seen,  or  otherwise  proved,  to  come  into  existence  except 
through  the  agency  of  already  existing  protoplasm.  All  life 
comes  from  life.  All  those  former  behefs  of  spontaneous 
appearance   of   bees   from   the   carcasses   of   oxen,    flies   from 

decaying  flesh,  hair  worms 
from  horse  tail  hairs  in 
water  troughs,  and  bacteiia 
and  infusoria  in  infusions 
of  beef  or  hav  have  been 
shown  on  scientific  investi- 
gation to  be  utterly  v.ith- 
out  basis  of  fact. 

But  if  protoplasm  and 
life  do  not  appear,  are  not 
being  generated  spontane- 
ousl}^  in  this  earth  epoch, 
may  they  not  have  been 
in  earlier  ages?  Geologists 
and  biologists  attemipt  to 
explain  most  of  the  things 
that  happened  in  earlier 
geologic  ages  by  vvdiat  they 
observe  to  be  happening 
nov\\  Thev  would  answer, 
on  this  basis,  that  what 
e\^dence  we  now  have 
should  lead  us  to  believe 
that  the  generation  of  life  has  never  occurred.  But  there  must 
have  been  a  beginning.  Life  has  not  always  been.  The  ac- 
cepted geological  theory  of  the  making  of  om'  earth  precludes 
the  existence  of  life  on  it  until  the  globe  was  cool  enough  for 
organisms  to  exist.  We  know  that  there  is  a  maximum  of 
temperature  beyond  which  protoplasm  inevitably  coagulates. 
When  and  where  was  this  beginning  of  life?  The  biologist  can- 
not admit  spontaneous  generation  in  the  face  of  the  scientific 
evidence  he  has.  On  the  other  hand  he  has  difficulty  in  under- 
standing how  life  could  have  originated  in  any  other  way  than 
through  some  sort  of  transformation  from  inorganic  matter. 
As  a  matter  of  curiosity  we  may  glance  at  a  few  of  the 


Fig.  32. — Ascidian  or  sea  squirt. 


LIFE,  ITS  PHYSICAL  BASIS  AND  SIMPLEST  EXPRESSION     43 


Fig.  33. — Blacksnake,  Bascanion  constrictor.     (Photograph  by  W.  H.  Fisher.) 


iiG.  6-i. — iiuwkoui  turtle,  Eretmochehjs  iitibricafa. 


44 


EVOLUTION   AND   ANIMAL   LIFE 


speculations  that  biologists  have  allowed  themselves  concerning 
the  origin  of  living  substance  on  the  earth.  A  speculation  that 
is  interesting  only  because  it  was  suggested  by  a  great  scientific 


Fig.  35. — Golden  eagle,  Aquila  chrysaetus. 


man — a  physicist,  however,  not  a  biologist — is  Lord  Kelvin's 
theory  that  living  substance  was  brought  to  this  earth  from 
celestial  regions  by  meteorites.  A  more  acceptable  theory  is 
that  at  some  earlier  geologic  age  the  conditions  of  earth,  atmos- 
phere, temperature,  etc.,  were  at  one  time  of  such  a  favorable 


IJFE,  ITS   PHYSICAL  BASIS  AND  SIMPLEST  EXPRESSION    45 

nature  that  just  that  fortunate  coincidence  of  all  necessary  con- 
ditions and  elements  occurred  which  allowed  C,  II,  O,  X,  to  unite 
in  those  great,  almost  infinitely  complex,  molecules  which  com- 
pose the  alljuminous  compounds  whose  existence  is  tlie  only  real 
chemical  characteristic  peculiar  to  living  matter.     But  we  have 


Fig.   36. — African  or  lw..-toed  ostrich,  Struthio  mmrhis.      (I'liotograph  by  William 

Graham.) 


46 


EVOLUTION   AND   ANIMAL   LIFE 


already  indicated  that  the  production  of  such  compounds  would 
not  necessarily  be  the  production  of  protoplasm.  What  of  the 
complex  definitive  physical  organization  of  protoplasm  on 
which  we  predicate  so  much  of  its  capacity? 

The  botanist  Schaffhausen  believes  that  water,  air,  and  the 
necessary  mineral  substances  have  been  directly  combined  under 
the  influences  of  hfe  and  heat  and  have  given  birth  to  an 


Fig.  37. — Opossum,  Didelphys  virginiana.     (One-tenth  natural   size;   photograph  by 

W.  H.  Fisher.) 


uncolored  protococcus  which  next  became  Protococcus  viridis.' 
Delage  asks :  "  If  the  thing  is  so  simple  why  does  not  the  author 
produce  one  of  these  protococci  in  his  laboratory?  On  lid  ferait 
grace  de  la  chlorophylle  I  "  Nageli  holds  that  when  the  albumi- 
nous compounds  had  their  birth  in  an  aqueous  liquid,  as  they 
were  not  soluble  in  water,  they  were  precipitated.  This  pre- 
cipitate was  formed  of  minute  particles,  a  sort  of  crystal  which 
he  calls  micellae.  These  micellae  are  the  materials  from  which 
organisms  were  formed.  An  inorganic  crystal  deposited  in  a 
saturated  solution  of  the  same  nature  determines  a  deposit 
on  its  surface  in  the  form  of  tiny  crystals,  by  which  means  it 


LIFE,  ITS  PHYSICAL  BASIS  AND  SIMPLEST  EXPRESSION   47 

increases  in  size.  In  the  same  way,  when  some  of  these  an)u- 
minous  micellse  are  formed  anywliere,  they  facihtate  further 
precipitation  within  their  sphere  of  influence  in  such  a  way  that 
the  formation  of  other  micella),  instead  of  going  on  uniformly 
in  the  liquid  mass,  is  localized  at  certain  points.  Thus  are 
found  aggregates  of  an  albuminous  nature  which  constitute  tlie 
primitive  protoplasm.  This  is  Niigeli's  suggestion,  and  Xiigcli 
is  one  of  the  most  thoughtful  biologists  wlio  has  ever  lived! 

Granting  that  protoplasm  must  have  had  a  natural,  spon- 
taneous beginning  on  this  earth,  being  neitlier  l^rought  to  it 
from  other  worlds  nor  created  extranaturally  on  this  world, 
biologists  indulge  in  some  speculations  as  to  the  proljal)le 
whereabouts  of  this  first  appearance  of  life,  and  as  to  whether 
living  substance  was  formed  spontaneously  but  once  only  or 
several  times,  and  perhaps  in  several  places.  It  is  not  necessary 
here  to  follow  up  such  speculations.  The  only  one  of  them  with 
any  scientific  evidence  at  all  for  it  is  the  theory  that  hfe  began 
at  the  poles  or  perhaps  particularly  at  the  north  pole.  The 
evidence  for  this  is  based,  first,  on  the  fact  that  in  accordance 
with  the  cosmic  theory  of  world  evolution,  the  poles  of  the 
earth  must  have  been  fu-st  in  a  condition  under  which  life  might 
exist,  and,  second,  on  facts  revealed  by  the  study  of  the  geo- 
graphical distribution  of  living  and  fossil  organisms.  There 
seems  to  be  some  slight  scientific  foundation  for  the  claim  that 
the  first  organisms  lived  in  polar  regions. 


50  EVOLUTION   AND   ANIMAL   LIFE 

alike.  This  refers  not  only  to  individuals  of  different  species 
of  plants  and  animals,  but  to  individuals  of  the  same  species 
and  even  (and  this  in  a  way  is  most  important  of  all)  to  indi- 
viduals born  of  the  same  parents.  It  is  indeed  this  last  condi- 
tion that  is  the  actual  basis  and  fundamental  beginning  for 
species  change.  That  this  variation  does  exist  is  absolute  fact, 
and  there  is  no  discussion  of  it. 

To  what  extent  or  degree,  what  parts  of  an  organism  are 
chiefly  affected,  whether  or  no  tliis  variation  shows  a  regularity 
in  its  occurrence  or  a  determinateness  of  tendency  or  direction, 
whether  or  no  this  variation  is  based  on  inheritance  and  if  so 
in  what  degree  of  similaritvor  iclentitv — all  these  and  a  dozen 
other  questions  are  the  moot  problems  in  connection  with  the 
great  factor  variation.  These  are  undecided  things,  which 
means,  on  the  whole,  that  variation,  apart  from  the  observed 
and  admitted  actuality  of  the  occurrence,  is  itself  a  great 
evolution  problem. 

The  variation  alone,  however,  presumably  does  not  make 
new  species  nor  maintain  lines  of  descent.  If  this  variation  is, 
as  it  seems  to  be,  almost  unlimited  in  its  range  of  appearance, 
then  as  species  are  of  definite  character  and  number  and  as  lines 
of  descent  are  even  more  definite  and  more  limited  as  to  number, 
there  must  be  some  factor  which  determines  what  kinds  or  lines 
of  variation  may  or  shall  persist  and  what  shall  be  extinguished. 
Is  there  something  incident  to  the  causes  of  variation  that 
determines  what  lines  of  descent  shall  be  established  by  it  or 
based  on  it,  or  is  there  some  added  factor  which,  having  no 
control  over  the  initial  appearance  of  variation,  has  absolute 
control  over  its  persistence  and  headway?  Darwin^s  factors  of 
selection,  more  particular^  natural  selection,  is  the  explanation 
of  this  control  offered  in  the  famous  "QrJgin  of  Species.^'  And 
natural  selection  has  been  in  the  minds  of  biologists  until  to-day, 
at  least,  undoubtedly  that  factor  in  evolution  which  has  been 
believed  to  have  the  chief  control  in  the  forming  of  species  and 
the  direction  of  descent  lines. 

But  in  reference  to  this  particular  factor  three  schools  of 
biologists  have  gradually  grown  up;  namely,  first  the  school 
headed  by  Weismann,  who  has  believed  and  contended  that 
natural  selection  is  almost  the  only  factor  which,  on  a  basis  of 
fortuitous,  that  is,  uncontrolled,  variation,  has  produced  the 
species  and  lines  of  descent  as  we  know  them;  second;  the 


FACTORS  AND  MECHANISM  OF  EVOLUTION  51 

school  which  holds  that  natural  selection  has  practically  nothin<^ 
to  do  with  species-forming  but  only,  and  in  a  large  general  way, 
with  the  control  of  descent;  and,  third,  the  compromise  school, 
which  attributes  to  natural  selection  an  important  part  in  both, 
species-forming  and  control  of  general  descent  lines,  but  recog- 
nizes the  simultaneous  existence  and  the  considerable  im- 
portance of  several  other  species-forming  and  descent-modifying 
factors.  In  addition  to  these  three  schools  one  must  note  that 
a  number  of  active  working  biologists  repudiate  the  factor  of 
natural  selection  entirely,  holding  it  to  be  a  vagary  and  an 
artifact  of  logic. 

Associated  with  natural  selection  in  the  general  theory  of 
selective  action  is  Darwin's  conception  of  sexual  selection.  Tliis 
factor  was  presumed  by  Darwin  to  play  a  part  only  in  the  forma- 
tion and  control  of  those  often  very  obvious  but  never  well- 
understood  characteristics  of  a  secondary  sexual  character 
w^iich  distinguish  the  sexes  in  many  species  of  animals.  Let 
one  recall  these  characters  in  the  pea  fowl,  the  bird  of  paradise, 
the  pheasant,  some  of  the  butterflies,  the  lamellicorn  beetles, 
many  fishes,  and  so  on.  According  to  the  theory  of  sexual 
selection  the  females  have  chosen  for  their  consorts  those  males 
best  endowed  by  variation  with  these  ornamental  character- 
istics, so  that  by  this  selection  there  has  come  about  a  gradual 
cumulation  of  the  characteristics  culminating  in  such  bizarrerie 
as  we  are  familiar  with  in  numerous  living  animals. 

The  word  selection  will  certainly  bring  to  the  mind  of  the 
reader  also  a  third  kind  of  selective  process,  namely,  that  called 
artificial  selection,  and  this  kind  of  selection  is,  of  course,  a 
factor,  and  an  important  one,  and  has  been  such  for  some  eighty 
centuries,  in  the  modification  of  plant  and  animal  forms.  But 
however  widely  differing  and  extraordinarily  modified  culti- 
vated and  domesticated  kinds  of  animals  and  plants  may  be, 
these  different  kinds  are  not  looked  on  by  biologists  as  having  the 
validity,  that  is,  the  stabilit}'  and  characteristics  of  origin,  that 
the  different  species  of  animals  and  plants  found  in  nature  have. 

All  the  different  kinds  of  pigeons,  for  example,  are  known  to 
be  due  primarily  to  the  artificial  modification  of  a  single  wild 
kind,  the  rock  dove  of  Europe,  and  all  of  these  different  artifi- 
cially produced  kinds  agree  in  an  important  physiological  charac- 
teristic, namely,  that  of  being  able  to  mate  freely  with  each  other 
and  with  their  common  ancestor.     As  this  physiological  char- 


52  EVOLUTION  AND  ANIMAL  LIFE 

acteristic  is  precisely  one  of  the  ciiteria  largely  used  in  deter- 
mining species  limits  in  natm'e,  natm-alists  call  the  artificially 
produced  kinds  by  another  name  than  species;  they  call  them 
races  or  varieties,  meaning  by  this  to  indicate  obvious  struc- 
tural and  functional  differences.  Thus  artificial  selection,  while 
a  factor  in  determining  the  extent  and  character  of  the  modifi- 
cation of  many  kinds  of  animals  and  plants,  is  not  considered  a 
factor  in  the  determination  of  natural  lines  of  descent.  Its 
value  in  this  regard  lies  in  the  clew  it  gives  to  natural  processes 
of  the  same  kind. 

Selection  by  nature  among  the  variations  which  appear  is 
made  possible  only  by  several  other  factors  or  actually  existent 
conditions.  One  is  the  "prodigality  of  production"  or  the 
constant  tendency  to  overpopulation  due  to  reproduction  by 
multiplication  or  in  a  geometrically  progressive  ratio.  Every 
mature  female  or  hermaphroditic  plant  or  animal  produces, 
at  least  in  the  condition  of  eggs  or  germ  cells,  more  than  one 
new  individual  like  itself.  (There  are  a  very  few  exceptional 
cases,  compensated  for,  however,  in  other  ways.)  Most  produce 
manv  new  individuals  and  some  reproduce  enormouslv.  Cer- 
tain  fishes  lay  millions  of  eggs;  so  do  certain  oysters;  many 
insects  produce  thousands  of  young;  many  plants  produce 
myriads  of  seeds.  But  not  all  can  grow  up:  there  is  neither 
room  nor  food  for  all.  There  must  inevitably  be  a  selection  by 
active  or  passive,  guided  or  fortuitous,  means. 

-  It  is  a  necessary  assumption,  for  the  effectiveness  of  the 
natural  selection  factor,  that  this  selection  is  actually  based  on 
the  fitness  or  advantage  of  some  of  the  A^ariations  as  compared 
with  others.  The  trying  out  or  determination  of  the  advantage 
of  these  variations  comes  about  as  an  inevitable  active  or  passive 
competition  for  life  among  the  overabundantly  appearing  new 
individuals.  This  is  the  "struggle  for  existence,''  and  the 
"survival  of  the  fittest"  is  the  expression  of  the  assumed  fact 
of  the  success  of  the  individuals  advantageously  (i.  e.,  most 
fitly)  varying.  The  unfit  and  the  less  fit  are  assumed  to  com- 
pose the  thousands  and  hundreds  of  thousands  who  must  die 
where  only  tens  or  hundreds  can  live  at  one  time. 

But  if  natural  selection,  which  is,  so  far,  obviously  one 
of  but  individuals  alone,  is  to  produce  new  species  and  control 
descent  lines,  it  has  to  depend  on  a  further  factor,  one  named  by 
a  familiar  word,  but  not  at  all  explained  by  it,  namely,  the  factor 


FACTORS   AND  MECHANISM   OF  EVOLUTIOX  5;^ 

heredity.  Although  we  can  rely  in  our  theory  ])uil(ling  on  the 
fact  that  no  two  individuals  are  exactly  alike,  yet  we  can  efiuaUy 
certainly  rely  on  the  fact  that  the  offspring  of  any  imhvidual 
will  be  much  more  like  other  individuals  of  the  species  to  which 
the  parent  belongs  than  like  individuals  of  other  species,  and 
also,  in  the  main,  more  like  the  parent  than  like  other  indi- 
viduals of  the  same  species.  Heredity  is  the  name  we  use  for 
expressing  this  fact  of  likeness  of  young  to  parent. 

Some  biologists  seem  to  mean  by  heredity  a  force  or  dominat- 
ing influence  which  brings  about  this  likeness;  while  others  use 
the  word  heredity  to  name  rather  the  processes  which  are  gone 
througli  with  by  the  young  in  becoming,  in  its  total  dcveloj)- 
ment,  like  the  parent.  The  essential  connotation  of  the  word 
is,  however,  simply  the  fact  that  this  likeness  does  exist  and  that 
we  ma}^  rely  on  its  continuing  to  occur.  So  that  when  the 
struggle  for  existence  w^eeds  out,  if  it  does,  those  individuals 
of  a  too  abundant  population  which  possess  variations  of 
disadvantage  or  of  no  special  advantage,  leaving  those  to 
survive  and  produce  offspring  which  do  possess  specially 
advantageous  or  fit  variations,  the  fact  of  heredity  permits  us 
to  assume  the  almost  certain  perpetuation  of  these  advan- 
tageous variations  by  insuring  their  reappearance  in  the  off- 
spring of  the  "  saved '^  individuals.  Thus  while  we  may  liken 
the  causes  that  produce  ever-appearing  variations  to  a  centrif- 
ugal force  making  for  difference  and  instabilit}^  heredity  (if 
used  as  the  name  for  the  causes  that  produce  likeness)  may 
be  conceived  as  a  centripetal  force,  making  for  stability  and 
sameness. 

But  at  least  one  other  factor  seems  to  be  necessary  in 
species-forming  and  that  is  the  factor  of  isolation,  separation, 
or  segregation,  as  it  is  variously  named.  By  this  is  meant  that 
those  individuals  showing  similar  variations  must  in  some  way 
be  segregated,  made  to  live  and  breed  together,  in  order  that  the 
particular  variations  (which  from  the  point  of  view  of  the 
student  of  species-forming  may  be  called  also  the  i)articular 
varietal  differences  that  are  to  become  in  time  so  developed  and 
fixed  as  to  be  true  species  differences)  may  be  maintained. 

For  it  is  obvious  that  if  an  individual  possessing  certain 

particular  variations  mate  witli  another  of  its  species  possessing 

different  variations,  the  offspring  of  this  union  will  likely  not 

possess  in  pure  form  the  variations  of  that  particular  parent 

5 


54  EVOLUTION  AND  ANIMAL  LIFE 

we  are  for  the  moment  interested  in.  The  offspring  may  sliow 
a  blend  of  the  different  characters  of  the  parents,  or  a  mosaic 
of  them,  or  may  show  the  characters  of  either  one  alone,  or, 
indeed,  characters  of  wholly  new  type.  The  important  thing 
is,  however,  that  there  is  no  certainty — indeed  there  is  almost 
certainty  of  the  opposite — that  any  particular  variation  will  be 
fostered  and  fixed  if  miscellaneous  interbreeding  is  allowed. 
So  that  a  segregation  of  individuals  having  certain  common 
variations  or  varietal  characters  is  necessary  for  the  perpetua- 
tion of  these  characters. 

Now  the  most  usual  way,  probably,  in  which  this  segregation 
or  isolation  is  brought  about  is  by  topographic  or  geographic 
barriers ;  a  group  of  individuals  gets  isolated  from  others  of  their 
species  by  some  physical  barrier,  and  the  variations  that  appear 
among  them,  due  often  to  some  cause  incident  to  the  special 
locality  and  hence  common  to  all  of  them,  are  readily  preserved 
and  fostered  by  the  enforced  breeding  among  themselves. 
But  such  an  isolation  may  conceivably  be  brought  about  in 
several  other  ways,  and  observation  has  shown  that  probably  in 
some  cases  so-called  biologic  isolation  occurs,  that  is,  that  a 
restriction  of  miscellaneous  interbreeding  among  individuals  of 
one  species,  and  an  enforced  selective  breeding  among  certain 
ones  possessing  certain  variations  or  differences  in  common, 
does  really  obtain.  Such  isolation  is  also  called  physiologic,  or 
sexual,  isolation. 

Many  biologists,  and  the  number  of  them  has  increased 
rapidly  in  the  last  few  years,  due  primarily  to  the  activity  and 
leadership  of  the  botanist  de  Vries  (Amsterdam),  believe  that 
species-forming  is  achieved  without  the  aid  of  the  selection 
factor;  that  the  actual  production  of  species  is  a  function  of 
variation  ("mutation"  the  special  kind  of  variation  efficient 
in  species-making  is  called),  and  that  the  influence  of  selection 
is  only  of  a  more  remote  and  generally  restraining,  and  thus 
directive,  nature.  Such  biologists  may  be  said  to  believe  in 
species-forming  by  heterogenesis  or  saltation,  as  contrasted 
with  species-making  by  slow,  gradual  transmutation.  And 
de  Vries  and  his  followers  have  adduced  a  few  apparently 
undeniable  examples  of  species-forming  by  heterogenesis.  At 
least  this  influence  seems  to  have  produced  forms  to  all  in- 
tents and  purposes  apparently  similar  to  natural  species.  So 
the  particular  kind  of  variation  called  mutation,  which  is  the 


Factors  and  mechanism  of  evolution         55 

liasis  of  this  sort  of  species-makings  must  Ije  added  to  our  list 
of  evolution  factors. 

Some  other  biolof^ists,  of  whom  the  botanist  Xii^oli,  the 
zoologist  Eimer,  and  the  paleontologist  CojDe  are  rei)resenta- 
tives  (all  three  of  these  men,  however,  having  evolution  theories 
and  beliefs  distinct  .and  peculiar  to  each),  believe  in  what  may 
be  called  orthogenetic  evolution.  That  is,  that  the  lines  of 
descent  are  determined  by  the  ai)pearance  of  certain  special 
determinate  lines  or  tendencies  of  variation  or  change,  this  non- 
fortuitous  and  determinate  variation  being  itself  determined 
by  certain  causes  either  (in  Niigeli's  l)elicf)  inherent  in  life,  or 
(in  Elmer's  belief)  extrinsic  to  life  but  imposed  upon  it,  as  for 
example  the  influence  of  climate,  etc.  So  that  orthogenesis  or 
determinate  variation  should  also  find  a  place  in  any  list  of 
assumed  evolution  factors. 

While  it  is  apparent  that  variation  is  ever  present  and  also 
apparent  that  heredity  or  the  fact  of  likeness  is  always  ever  to 
be  rehed  on,  the  exact  relationship  or  correlation  of  these  two 
evolution  factors  is  not  so  apparent.  That  heredity  often 
preserves  or  perpetuates  variations  after  they  have  occurred  is 
well  proved,  but  it  is  also  proved  that  some  variations  appearing 
in  the  parent  are  not  handed  on  to  the  parent's  offspring,  nor 
indeed  to  any  future  generations  of  the  line.  And  the  general 
answer  to  the  natural  query  raised  by  this  condition  is  that 
variations  which  are  congenital  or  blastogenic,  that  is,  are 
determined  at  birth  for  it  (although  they  appear  of  course  only 
after  development),  are  heritable  (that  is,  will  be  passed  on 
from  parent  to  offspring);  but  that  variations  or  modifications 
acquired  xluring  the  lifetime  of  the  individual,  that  is,  those  which 
are  impressed  on  it  by  extrinsic  influences  during  its  "growing 
up ''  or  development,  will  not  be  heritable.  Thus  such  modifica- 
tions in  body  parts  as  may  be  produced  b}^  use  or  disuse,  or  by 
other  functional  stimulation  or  lack  of  it,  changes  caused  by 
mutilation  or  disease,  etc.,  are  believed  by  most  biologists  to  be 
non-heritable.  Hence  it  is  that  only  the  congenital  variations 
are  looked  on  by  these  biologists  as  of  importance  in  the  matter 
jf  species-forming.  Yet  the  whole  pre-Darwinian  evolution 
theory  of  Lamarck  was  founded  on  the  assumption  that  the 
modifications  in  individuals  due  to  use,  disuse,  and  other  func- 
tional stimulation,  in  a  word  that  all  body  change  and  adapta- 
tion; all  characters  acquired  during  the  lifetime  of  an  individual; 


56  EVOLUTION   AND  ANIMAL   LIFE 

can  be,  in  some  degree  at  least,  handed  on  by  inheritance  to  the 
offspring.  And  there  are  to-day  many  Lamarckian  evohi- 
tionists.  So  that  in  our  hst  of  possible  evolution  factors  the 
so-called  Lamarckian  factor  should  not  be  omitted.  And  in 
connection  with  it  may  be  considered,  by  and  large,  the  imme- 
diate influence  or  non-influence  on  individuals  and  on  species 
of  all  environmental  conditions;  and  particularly  the  results 
of  such  influence  during  development.  In  fact  the  study  of 
development  has  come  largel}^  to  be  a  study  of  the  actual  in- 
fluences or  factors  that  determine  and  guide  growth,  instead  of 
one  purely  descriptive  and  comparative  as  in  the  older  days 
of  embryological  study.  Some  of  these  factors  are  apparently 
strictly  inherent  in  the  protoplasmic  germ  cells  and  in  the 
embryo  substance:  others  are  as  obviously  extrinsic  or  epigenetic. 
And  the  determination  of  the  relative  influence  and  power  of 
these  two  sets  of  developmental  factors  and  of  the  various 
members  of  each  set  is  one  of  the  most  eagerly  worked-at 
problems  of  modern  biological  stud}^ 

Finally,  the  general  term  adaptation  should  be  mentioned 
in  any  list  of  evolution  factors;  although  it  is  more  usually 
looked  on,  not  as  a  factor,  but  as  an  evolution  problem  and 
indeed  one  of  the  greatest  of  the  problems.  Adaptation  is 
precisely  one  of  the  things  evolutionists  are  trying  to  find  the 
causes  or  causal  factors  of.  But  nevertheless  the  adaptability 
of  life  stuff,  its  plasticity  and  capacity  of  advantageous  reac- 
tion, is,  to  many  biologists,  a  fundamental  fact  in  organic 
nature,  like  gravitation  or  chemical  affinity  in  inorganic  nature: 
a  thing  basic  and  inexplicable,  and  in  itself  a  factor  whose  con- 
sequences are  to  be  determined  but  not  further  to  be  ques- 
tioned as  to  their  cause. 


CHAPTER  V 

NATURAL  SELECTION   AND  THE   STRUGGLE 
FOR    EXISTENCE;     SEXUAL  SELECTION 

The  tendency  to  regard  natural  selection  as  more  or  less  unnecessary 
or  superfluous  which  is  so  characteristic  of  our  day,  seems  to  grow  out 
of  reverence  for  the  all-sufficiency  of  the  philoso])hy  of  evolution,  and 
pious  belief  that  the  history  of  li\dng  things  flows  out  of  this  j^hilosophy 
as  a  necessary  truth  or  axiom. — Brooks. 

La  selection  naturelle  est  un  principe  admirable  et  parfaitement 
juste.  Tout  le  monde  est  d'accord  aujourdliui  sur  ce  point.  Mais 
oil  Ton  n'est  pas  d'accord,  c'est  sur  la  liniite  de  sa  puissance  et  sur  la 
question  de  savoir  si  elle  peut  engendrer  des  formes  specifiques 
nouvelles.     II  semble  bien  demontre  aujourd'hui  qu'elle  ne  le  i:)eut. 

— Delage. 

Of  all  the  various  factors  of  organic  evolution  the  one 
which  has  been  most  relied  on  as  the  great  determining  agent 
is  that  called  Natural  Selection,  the  survival  of  the  individuals 
best  fitted  for  the  conditions  of  life,  with  the  inheritance  of 
those  species-forming  adaptations  in  which  fitness  lies.  The 
primal  initiative  is  not  in  natural  selection,  but  in  variation, 
germinal  and  individual.  This  may  be  slight  variation  (fluc- 
tuation) or  large  deviation  (saltation),  but  in  an}-  case  all 
difference  in  species  or  race  must  first  be  individi'al.  The 
impulse  to  change,  once  arisen,  is  continued  through  lierodity. 
From  natural  selection  arises  the  choice  among  different  lines 
of  descent,  the  ada])tive  tending  to  exclude  the  non-adaptive, 
while  traits  which  are  neither  helpful  nor  hurtful,  but  simply 
indifferent,  may  be  borne  along  by  the  current  of  adaptive 
characters.  Finally  separation  or  isolation  tends  to  preserve  a 
special  line  of  heredity  from  being  merged  in  the  mass  which 
constitutes  the  parent  stock  or  species. 

Without  individual  variation,  no  change  could  take  j^laco; 
all  organisms  would  be  identical  in  structure.    Without  heredity, 

57 


58  KVOLUTIOX   AND   ANIMAL   LIFE 

if  we  could  conceive  such  a  condition,  no  change  would  persist. 
Without  selection,  there  would  be  no'  premium  placed  on 
adaptive  characters,  and  organisms  would  persist  in  every 
degree  of  variance  with  their  surroundings.  Without  some 
degree  of  isolation,  every  change  would  be  lost  by  cross-breeding 
with  the  mass.  In  a  world  of  varying  conditions  with  varying 
organisms,  it  is  not  conceivable  that  species  should,  through 
all  their  generations,  undergo  no  change.  Nor  in  the  changes 
of  any  species  is  it  possible  that  any  one  of  the  factors  or  con- 
ditions named  above  should  be  wholly  absent.  But  the  effects 
of  each  one  ma}''  show  themselves  in  many  different  waj^s,  and 
each  may  be  modified  by  other  facts  or  conditions.  We  have 
compared  the  history  of  species  to  the  flow  of  a  river.  A  single 
rock  may  change  the  course  of  a  stream.  In  like  manner 
incidental  circumstances  may  determine  the  evolution  of  a 
species.  Or  using  a  different  metaphor  we  may  compare  the 
course  of  a  species  with  that  of  a  glacier.  The  movement  of  a 
glacier  depends  on  the  law  of  gravitation  "resident"  within 
its  molecules.  Its  course  is  determined  by  th^  topography  of 
its  bed.  To  this  bed  it  is  perfectly  fitted,  but  the  condition  of 
its  surface  depends  on  circumstances  related  neither  to  the  law 
of  gravitation  nor  to  the  form  of  its  bed.  A  species  of  animal  or 
plant  is  well  fitted  to  its  conditions  in  life.  This  natural 
selection  rigidly  enforces ;  but  its  surface  characters,  which  are 
not  essential  to  its  life,  are  determined  by  other  influences,  and 
in  this  both  selection  and  environment  play  but  a  minor  part. 

All  animals  feed  upon  living  organisms  or  upon  that  Avhich 
has  been  living.  Hence  each  animal  throughout  its  life  is  busy 
with  the  destruction  of  the  other  organisms  or  with  their 
removal  after  death.  If  these  creatures,  animals,  or  plants  on 
which  animals  feed,  are  to  hold  their  own,  there  nmst  be  an 
excess  of  birth  and  development  to  make  good  the  drain  upon 
their  numbers.  If  the  plants  did  not  restore  their  losses  the 
animals  that  feed  on  them  would  perish.  In  like  fashion  flesh- 
eating  animals  are  dependent  on  those  which  feed  on  plants. 

But  throughout  nature  there  is  a  vast  excess  in  the  process 
of  reproduction.  More  plants  sprout  than  could  find  standing 
room  were  all  to  grow.  More  seeds  are  developed  than  can  find 
place  to  sprout.  More  animals  are  born  than  can  possibly 
survive.  The  process  of  increase  among  animals  is  rightly 
called  multiplication.     Each  species  tends  to  increase  in  geo- 


NATURAL  SELECTION;  SEXUAL   SELECTION  59 

metric  ratio,  but  as  it  multiplies  it  finds  the  world  already 
crowded  with  other  multiplying  species.  A  single  pair  of  any 
species  whatsoever,  if  not  checked  by  adverse  conditions,  would 
soon  fill  the  whole  earth  with  its  progeny. 

An  annual  plant  producing  two  seeds  only  would  have 
1,048,576  descendants  in  twenty-one  years,  if  each  seed  sprouted 
and  matured.  But  most  plants  produce  hundreds  or  thousands 
of  seeds.  The  ratio  of  increase  is  a  matter  of  minor  imj)ortance. 
It  is  the  ratio  of  increase  above  loss  whicli  determines  tlie  fate 
of  species.  Those  species  increase  in  numbers  in  wliicli  the 
gain  exceeds  the  rate  of  destruction  througli  the  influence  of 
other  species  or  the  adverse  conditions  of  life.  Where  few 
enemies  exist  the  ratio  of  increase  need  not  be  large.  One  of 
the  most  abundant  of  birds  is  the  fulmar  petrel  of  the  mid- 
Pacific.  It  lays  but  one  egg  yearly,  but  it  has  few  enemies  and 
the  low  rate  of  increase  suffices  to  cover  the  sea  with  fulmars 
within  the  region  it  inhabits. 

It  is  not  easy  to  realize  the  inordinate  numbers  any  species 
would  attain  were  it  not  for  the  checks  produced  by  the  presence 
of  the  activity  of  other  organisms.  Certain  protozoa,  at  their 
normal  rate  of  increase — if  none  were  devoured  or  destroyed — 
might  fill  the  entire  ocean  within  a  very  short  time.  It  is  said 
that  the  conger  eel  lays  15,000,000  eggs  yearly.  If  each  hatched 
and  the  conger  grew  to  maturity,  in  a  few  years  there  would  be 
no  room  for  any  other  kind  of  fish  in  the  sea.  The  codfish  has 
been  known  to  produce  9,100,000  eggs  each  year.  If  each  egg 
were  to  develop,  in  ten  years  the  sea  would  be  solidly  full  of 
codfish. 

The  female  quinnat  salmon  of  the  Columbia,  Oncorhynchus 
tchamytscha,  ascends  the  river  at  the  age  of  about  four  years, 
and  lays  4,000  eggs,  after  which  she  dies.  Half  these  eggs 
develop  into  males.  If  each  female  egg  came  to  maturity,  we 
should  have  at  the  end  of  fifty  years  8,000,000,000,000,000,- 
000,000,000,000,000,000,000,000,000  female  salmon  and  as 
many  males  as  the  offspring  of  a  single  pair.  It  takes  al^out 
one  hundred  of  these  salmon  to  weigh  a  ton.  Could  all  these 
fishes  develop,  in  a  very  short  time  there  would  be  no  room 
for  them  in  all  the  I'ivers  c^  the  North,  nor  in  all  the  waters  of 
the  sea. 

If  each  egg  of  the  conmion  house  fly  slioiild  develop  and  each 
of  the  larva)  should  find  the  food   :nd  temperature  it  neech'd 


60  EVOLUTION   AND  ANIMAL   LIFE 

with  no  loss  and  no  destruction,  the  people  of  the  city  in  whie^ 
it  happened  would  suffocate  under  the  plague  of  flies.  When- 
ever any  species  of  insect  develops  a  large  percentage  of  the  egg€ 
laid,  it  becomes  at  once  a  plague.  Thus  originate  plagues  of 
locusts,  grasshoppers,  and  caterpillars.  But  the  crowd  of  life 
renders  these  plagues  rare.  Scavenger-beetles  and  bacteria 
destroy  the  decaying  flesh  where  the  fly  would  lay  its  eggs. 
IMinute  creatures,  bacteria,  protozoa,  other  insects,  are  parasitic 
within  the  larva  itself.  ]\lillions  of  flies  starve  to  death.  Mil- 
lions more  are  eaten  by  birds  and  predaceous  insects.  The 
final  result  is  that  from  year  to  year  the  number  of  flies  does 
not  increase.  Linnaeus  once  said  that  "  three  flies  will  devour 
a  dead  horse  as  quickly  as  a  lion.^'  Quite  as  soon  would  three 
bacteria  with  their  descendants  reach  the  same  result.  "Even 
slow-breeding  man,"  saj^s  Darwin,  "has  doubled  in  twenty-five 
years.  At  this  rate  in  less  than  a  thousand  vears  there  literally 
would  not  be  standing  room  for  his  progeny.  The  elephant  is 
reckoned  the  slowest  breeder  of  all  animals.  It  begins  breeding 
when  thirty  years  old  and  goes  on  breeding  until  ninet}^  years 
old,  bringing  forth  six  young  in  the  interval  and  surviving  to  be 
a  hundred  years  old.  If  this  be  so,  after  about  800  years  there 
should  be  19,000,000  elephants  alive  descended  from  the  first 
pair."  A  few  years  of  still  further  multiplication  without  check, 
and  every  foot  of  the  earth  would  be  covered  by  elephants. 

Similar  calculations  may  be  made  in  regard  to  any  species  of 
animal  or  plant  whatsoever.  Each  one  increases  at  a  rate  which 
without  checks  would  make  it  soon  cover  the  earth.  Yet  the 
number  of  individuals  in  a  state  of  nature  in  any  species  re- 
mains about  stationary.  With  the  interference  of  man,  in 
many  species  the  numbers  slowly  diminish;  very  few  increase. 
There  are  about  as  many  squirrels  in  the  forest  one  year  as 
another,  as  many  butterflies  in  the  field,  as  many  frogs  in  the 
pond.  Wolves,  bears,  deer,  ducks,  singing  birds,  fishes,  all  suf- 
fer from  man's  attacks  or  man's  neglect  and  grow  fewer  year 
by  year.  It  is  manifest  that  the  tendency  to  reproduce  by 
geometric  ratio  meets  everywhere  with  a  corresponding  check. 
This  check  is  known  as  the  Struggle  for  Existence. 

The  struggle  for  existence  is  threefold:  (a)  Among  indiAdduals 
of  one  species,  as  wolf  against  wolf  or  sparrow  against  sparrow, 
(b)  between  individuals  of  different  species,  as  rabbit  with  wolf 
or  blue-bird  with  sparrow ;  (c)  with  the  conditions  in  Uf e — as 


NATURAL   SELECTION;   SEXUAL  SELECTION 


61 


the  necessity  of  the  robin  to  find  water  in  summer  or  to  keep 
warm  in  winter.  All  three  forms  of  the  struggle  for  existence, 
intraspecific,  interspecific,  and  environmental,  are  constantly 
operative  and  with  every  species.  In  some  regions  or  under 
some  conditions  the  one  phase  may  be  more  destructive,  in 
others  another.  Any  one  of  these  may  ])e  in  various  ways 
modified  or  ameliorated.  When  the  conditions  of  life  are  most 
easy,  as  with  most  species  in  the  tropics,  tliere  the  conflict  of 
individuals  and  the  conflict  of  species  is  most  severe.  It  is  not 
possible  to  say  that  any  one  of  these  three  forms  of  struggle  and 
selection  is  more  potent  than  the  others.  In  fact,  the  first  and 
the  second  are  in  a  sense  forms  of  the  third.  All  struggle  is, 
strictly  speaking,  with  the  conditions  of  life.     Those  individuals 


Fig.  38. — Praying  mantis,  eating  a  grasshopper.     (Adapted  from  photograph 

from  Ufe  by  Slingerland.) 

which  endure  this  struggle  survive  to  reproduce  themselves. 
The  rest  die  and  leave  no  progeny. 

Because  of  the  destruction  resulting  from  the  struggle  for 
existence,  more  individuals  in  each  species  are  born  than  can 
mature.  The  majority  fail  to  reach  maturity  because  for  one 
reason  or  another  they  cannot  do  so.  All  live  that  can.  Each 
animal  tries  to  feed  itself:  many  try  to  take  care  of  their  young. 
But  in  self  protection  and  in  propagation  of  the  species  very  few 
individuals  succeed  in  comparison  with  the  vast  number  which 
the  process  of  reproduction  calls  into  being. 

The  destruction  in  nature  is  not  indiscriminate.  In  the 
long  run  and  for  the  most  part,  those  creatures  least  fitted  to 
resist  are  the  first  to  perish.  It  is  the  slowest  animal  wliich  is 
soonest  overtaken  by  the  pursuers.     It  is  the  weakest  which  is 


62 


EVOLUTION  AND  ANIMAL  LIFE 


crowded  aside  or  trampled  on  by  its  associates.  It  is  the  least 
adaptable  which  suffers  most  from  extremes  of  heat  and  cold. 
By  the  process  of  Artificial  Selection  the  breeder  improves  his 
stock,  destroying  his  weakest  or  least  comely  calves,  reserving 
the  strong  and  fit  for  parentage.  In  like  fashion,  on  an  in- 
conceivably large  scale,  the  forces  of  nature  are  at  work  modify- 
ing and  fitting  to  the  demands  of  their  surroundings  the  different 
species  of  animals.  Because  the  processes  and  results  of  the 
struggle  for  existence  seem  parallel  with  those  of  artificial 
selection,  Darwin  suggested  the  name  of  Natural  Selection 
for  the  sifting  process  as  seen  in  nature.  To  the  general  re- 
sult of  natural  selection,  Herbert  Spencer  has  applied  the  term 


fiG.  39. — The  Australian  ladybird,  Fe(faZja  cartfinaZis,  feeding  on  cottony  cushion  scale^ 

Icerya  purchasi.     (From  life.)  • 


Survival  of  the  Fittest.  By  fitness  in  this  sense  is  meant  only 
adaptation  to  surrounding  conditions,  for  the  process  of  natural 
selection  has  no  necessary  moral  element,  nor  does  it  necessarily 
work  toward  progress  among  organisms.  With  changing  con- 
ditions species  undergo  change.  Some  individuals,  by  the 
possession  of  slight  advantageous  variations  of  structure  or  of 
instinct,  meet  these  new  demands  better  than  others.  These 
survive,  the  others  die.  The  survivors  produce  young  sharing 
in  part,  at  least,  their  own  advantages,  and  with  renewed  selec- 
tion the  degree  of  adaptation  increases  with  successive  genera- 
tions. 

To  the  process  of  r_3.tural  selection  we  must,  in  most  cases, 
probably  ascribe  the  adjustment  of  species  to  surroundings 


Natural  selection;  sexual  selection         G3 

Natural  selection  does  not  create  species,  it  enforces  adaptation. 
If  a  species  or  a  group  of  individuals  cannot  fit  itself  to  its 
environment,  it  will  be  crowded  out  by  others  which  can  do  so. 
It  will  then  either  disappear  entirely  from  the  earth,  or  it  will  be 
Umited  to  that  region  or  to  those  conditions  to  wliicli  it  is 
adapted.  A  partial  adjustment  tends  to  become  more  perfect, 
for  ths  individuals  least  fitted  are  first  destroyed  in  the  struggle 
for  existence.  Very  small  variations  may  sometimes,  therefore 
lead  to  great  changes.  A  side  issue  apparently  unimportai- , 
may  perhaps  determine  the  fate  of  a  species.  Any  advantage 
however  small  may  possibly  turn  the  scale  of  life,  "l^attle 
within  battles  must  be  continually  recurring,  witli  varying  suc- 
cess, yet  in  the  long  run  the  forces  are  so  nicely  balanced  that 
the  face  of  nature  remains  for  a  long  time  uniform,  though 
assuredly  the  merest  trifle  w^ould  give  the  victory  to  one  organic 
being  over  another. '' 
Darwin  says: 

"  I  have  found  that  the  visits  of  bees  are  necessary  for  the  fertili- 
zation of  some  kinds  of  clover;  for  instance,  twenty  heads  of  white 
clover  {Trifolium  repens)  yielded  two  thousand  two  hundred  and  ninety 
seeds,  but  twenty  other  heads  protected  from  the  bees  produced  not 
one.  Again,  one  hundred  heads  of  red  clover  (Trifolium  pratensc) 
produced  two  thousand  seven  hundred  seeds,  but  the  same  number  of 
protected  heads  produced  not  a  single  seed.  Humble-bees  alone  visit 
red  clover,  as  other  bees  cannot  reach  the  nectar.  .  .  .  Hence  we  may 
infer  as  highly  probable  that,  if  the  whole  genus  of  humble-bees  became 
extinct  or  very  rare  in  England,  the  heartsease  and  red  clover  would 
become  very  rare  or  wholly  disappear.  The  number  of  humble-bees 
in  any  district  depends  in  a  great  measure  on  the  number  of  field  mice, 
which  destroy  their  combs  and  nests;  and  Colonel  Newman,  who  has 
long  attended  to  the  habits  of  humble-bees,  believes  that  more  than 
two-thirds  of  them  are  thus  destroyed  all  over  England.  Now  the 
number  of  mice  is  largely  dependent,  as  everyone  knows,  on  the  num- 
ber of  cats;  and  Colonel  Newonan  says:  'Near  villages  and  small  towns 
I  have  found  the  nests  of  humble-bees  more  numerous  than  else- 
where, which  I  attribute  to  the  number  of  cats  that  destroy  the  mice.' 
Hence  it  is  quite  credible  that  the  presence  of  feline  animals  in  large 
numbers  in  a  district  might  determine,  through  the  intervention 
first  of  mice  and  then  of  bees,  the  frequency  of  certain  flowers  in 
that  district." 


64  EVOLUTION  AKD  ANIMAL  LIFE 

Huxley  carries  this  calculation  still  further  by  showing  that 
the  number  of  cats  depends  on  the  number  of  unmarried  women. 
On  the  other  hand,  clover  produces  beef,  and  beef  strength. 
Thus  in  a  degree  the  prowess  of  England  is  related  to  the  number 
of  spinsters  in  its  rural  districts!  This  statement  would  be  true 
in  all  seriousness  w^ere  it  not  that  so  many  other  elements  come 
into  the  calculation.  But  w^hether  true  or  not,  it  illustrates  the 
way  in  w^hich  causes  and  effects  in  biology  become  intertangied. 

There  w^as  introduced  into  California  from  Australia,  on 
young  lemon  trees,  twenty-five  years  ago,  an  insect  pest  called 
the  cottony  cushion  scale  (Icerya  purchasi).  This  pest  in- 
creased in  numbers  with  extraordinary  rapidity,  and  in  ten  years 
threatened  to  destroy  completely  the  great  orange  orchards  of 
California.  Ai'tificial  remedies  were  of  little  avail.  Finally,  an 
entomologist  was  sent  to  Australia  to  find  out  if  this  scale  insect 
had  not  some  special  natural  enemy  in  its  native  country.  It  was 
found  that  in  Australia  a  certain  species  of  ladybird  beetle 
attacked  and  fed  on  the  cottony  cushion  scales  and  kept  them 
in  check  (Fig.  39).  Some  of  these  ladA^birds  {Vedalia  cardi- 
nalis)  were  brought  to  California  and  released  in  a  scale-infested 
orchard.  The  ladybirds,  having  plenty  of  food,  thrived  and 
produced  many  young.  Soon  they  were  in  such  numbers  that 
many  of  them  could  be  distributed  to  other  orchards.  In 
two  or  three  years  the  Vedalias  had  become  so  numerous 
and  mdety  distributed  that  the  cottony  cushion  scales  began 
to  diminish  perceptibly,  and  soon  the  pest  was  nearly 
wiped  out.  But  wdth  the  disappearance  of  the  scales  came 
also  a  disappearance  of  the  ladybirds,  and  it  was  then  dis- 
covered that  the  Vedalias  fed  only  on  cottony  cushion  scales 
and  could  not  live  where  the  scales  were  not.  So  now,  in  order 
to  have  a  stock  of  Vedalias  on  hand  in  California,  it  is  necessary 
to  keep  protected  some  colonies  of  the  cottony  cushion  scale 
to  serve  as  food.  Of  course,  with  the  disappearance  of  the  pre- 
daceous  ladybirds  the  scale  began  to  increase  again  in  various 
parts  of  the  State,  but  with  the  sending  of  Vedalias  to  these 
localities  the  scale  was  again  crushed.  How  close  is  the  inter- 
dependence of  these  two  species! 

There  is  little  foundation  for  the  current  belief  that  each 
species  of  animal  has  originated  in  the  area  it  now  occupies,  for 
in  many  cases  our  knowledge  of  palaeontology  show^s  the  reverse 
of  this  to  be  true.     Even  more  incorrect  is  the  belief  that  each 


NATURAL  SELECTION;   SEXUAL  SELECTION  65 

species  occupies  the  district  or  the  surroundings  best  fitted 
for  its  habitation.  This  is  manifested  in  the  fact  of  the  extraor- 
dinary fertihty  and  persistence  shown  In'  many  kinds  of  animals 
and  pkmts  in  taking  possession  of  new  lands  which  have  become, 
through  the  voluntary  or  involuntary  interference  of  man,  oj)en 
to  their  invasion.  Facts  of  this  sort  are  the  "enormous  in- 
crease of  rab])its  and  pigs  in  Australia  and  New  Zealand,  of 
horses  and  cattle  in  South  America,  and  of  the  sparrows  of 
North  America,  though  in  none  of  these  cases  are  the  animals 
natives  of  the  countries  in  which  they  thrive  so  well ''  (Wal- 
lace^). The  persistent  spreading  of  European  weeds  to  the 
exclusion  of  our  native  plants  is  a  fact  too  w-ell  known  to  every 
farmer  in  America.  The  constant  moving  w^estw^ard  of  the 
white  weed  and  the  Canada  thistle  marks  the  steady  deteriora- 
tion of  our  grass  fields.  The  cockroaches  in  American  kitch- 
ens represent  invading  species  from  Europe.  The  American 
cockroaches  Hve  in  the  woods.  Perhaps  a  majority  of  the 
worst  insect  pests  of  the  United  States  are  of  European  or 
Asiatic  origin.  Especially  noteworthy  are  cases  of  this  type 
in  Austraha  and  New  Zealand.  In  New  Zealand  the  weeds 
of  Europe,  toughened  by  centuries  of  selection,  have  won  an 
easy  victory  over  the  native  plants. 

Dr.  Hooker  states  that,  in  New^  Zealand  "  the  cow  grass  has 
taken  possession  of  the  roadsides;  dock  and  w^atercress  choke 
the  rivers;  the  sow  thistle  is  spread  all  over  the  country,  growing 
luxuriantly  up  to  6^000  feet;  white  clover  in  the  mountain  dis- 
tricts displaces  the  native  grasses. '^  The  native  Maori  saying 
is:  "As  the  white  man^s  rat  has  driven  away  the  native  rat,  as 
the  European  fly  drives  away  our  ow^n,  and  the  clover  kills  our 
fern,  so  will  the  Maoris  disappear  before  the  w^hite  man  himself." 

Prof.  Sidney  Dickinson  gives  the  follow^ing  notes  on  the 
rabbit  and  other  plagues  of  Australia: 

"The  average  annual  cost  to  Australasia  of  the  rabbit  i)lague  is 
£700,000,  or  nearly  $3,500,000.  The  work  which  these  enormous  figures 
represent  has  a  marked  effect  in  reducing  the  number  of  rabbits  in  the 
better  districts,  although  there  is  little  to  suppose  that  their  extermina- 
tion will  ever  be  more  than  partial.  Most  of  the  larger  runs  show  very 
few  at  present,  and  rabbit-proof  fencing,  which  has  been  sot  around 
thousands  of  square  miles,  has  done  much  to  cheek  further  inroads. 
Until  this  invention  began  to  be  utilized  it  was  not  uncommon  to  find 


66  EVOLUTION    AND  ANIMAL   LIFE 

as  many  as  a  hundred  rabbiters  employed  on  a  single  property  whose 
working  average  was  from  three  hundred  to  four  hundred  rabbits  per 
day.  As  they  received  five  shillings  a  hundred  from  the  station  owner, 
and  were  also  able  to  sell  the  skins  at  eight  shillings  a  hundred,  their 
profession  was  most  lucrative.  Seventy-five  dollars  a  week  was  not 
an  uncommon  wage,  and  many  an  unfortunate  squatter  looked  with 
envy  upon  the  rabbiters,  who  were  heaping  up  modest  fortunes,  while 
he  himself  was  slowly  being  eaten  out  of  house  and  home. 

''The  fecundity  of  the  rabbit  is  amazing,  and  his  invasion  of  remote 
districts  swift  and  mysterious.  Careful  estimates  show  that,  under 
favorable  conditions,  a  pair  of  Australian  rabbits  will  produce  six 
litters  a  year,  averaging  five  individuals  each.  As  the  offspring  them- 
selves begin  breeding  at  the  age  of  six  months,  it  is  shown  that,  at  this 
rate,  the  original  pair  might  be  responsible  in  five  years  for  a  progeny 
of  over  twenty  millions.  That  the  original  score  that  were  brought  to 
the  country  have  propagated  after  some  such  ratio,  no  one  can  doubt 
who  has  seen  the  enormous  hordes  that  now  devastate  the  land  in 
certain  districts.  In  all  but  the  remoter  sections,  the  rabbits  are  now 
fairly  under  control;  one  rabbiter  with  a  pack  of  dogs  supervises 
stations  where  one  hundred  were  employed  ten  years  ago,  and  with 
ordinary  vigilance  the  squatters  have  little  to  fear.  Millions  of  the 
animals  have  been  killed  by  fencing  in  the  water  holes  and  dams  during 
a  dry  season,  whereby  they  died  of  thirst,  and  lay  in  enormous 
piles  against  the  obstructions  they  had  frantically  and  vainly  striven 
to  climb,  and  poisoned  grain  and  fruit  have  killed  myriads  more.  A 
fortune  of  £25,000  offered  by  the  New  South  Wales  Government  still 
awaits  the  man  who  can  invent  some  means  of  general  destruction, 
and  the  knowledge  of  this  fact  has  brought  to  the  notice  of  the  various 
colonial  governments  some  very  original  devices. 

"Another  great  pest  to  the  squatters  is  developing  in  the  foxes, 
two  of  which  were  imported  from  Cumberland  some  years  ago  by  a 
wealthy  station  owner,  who  thought  that  they  might  breed,  and 
give  himself  and  friends  an  occasional  day  with  the  hounds.  His 
modest  desires  were  soon  met  in  the  development  of  a  race  of  foxes 
far  surpassing  the  English  variety  in  strength  and  aggressiveness, 
which  not  only  devour  many  sheep,  but  out  of  pure  depravity  worry 
and  kill  ten  times  as  many  as  they  can  eat.  When  to  these  plagues  is 
added  the  ruin  of  thousands  of  acres  from  the  spread  of  the  thistle, 
which  a  canny  Scot  brought  from  the  Highlands  to  keep  alive  in  his 
breast  the  memories  of  Wallace  and  Bruce;  the  well-nigh  resistless 
inroads  of  furze;  and,  in  New  Zealand,  the  blocking  up  of  river?  by 


NATURAL  SELECTIOX;  SEXUAL  SELECTION  67 

the  English  watercresS;  which  in  its  new  home  grows  a  dozen  feet  in 
length,  and  has  to  be  dredged  out  to  keep  navigation  open,  it  may  be 
understood  the  colonials  look  with  jaundiced  eye  upon  suggestions 
of  any  further  interference  with  Australian  nature. 

"Not  to  be  outdone  by  foreign  importations,  the  country  itself 
has  shown  in  the  humble  locust  a  nuisance  quite  as  potent  as  rabliit, 
fox,  or  thistle.  This  bane  of  all  men  who  pasture  sheep  on  grass  has 
not  been  much  in  evidence  until  within  the  last  few  years,  when 
the  great  destruction  of  indigenous  birds  by  the  gun  and  by  poisoned 
grain  strewn  for  rabbits  has  facilitated  its  increase.  The  devastation 
caused  by  these  insects  last  year  was  enormous,  and  befell  a  district  a 
thousand  miles  long  and  two  thousand  wide.  For  days  they  passed  in 
clouds  that  darkened  the  earth  with  the  gloomy  hue  of  an  eclipse, 
while  the  ground  was  covered  with  crawling  millions,  devouring  every 
green  thing  and  giving  to  the  country  the  appearance  of  being  carpeted 
with  scales.  It  has  been  discovered,  however,  that  before  they  attain 
their  winged  state  they  can  easily  be  destroyed,  and  energetic  measures 
will  be  taken  against  them  throughout  all  the  inhabited  districts  of 
Australia  whenever  they  make  another  appearance.'' 

The  conditions  of  the  struggle  for  existence  are  not  neces- 
sarily felt  as  an  individual  stress  to  the  individuals  which  sur- 
vive. The  life  the}"  lead  is  the  one  for  which  they  are  fitted. 
The  struggle  is  painfid  or  destructive  only  to  those  imperfectly 
adapted.  ^len  in  general  are  fitted  to  the  struggle  endured  by 
their  ancestors  as  they  are  adapted  to  the  pressure  of  the  air. 
They  do  not  recognize  the  pressure  itself  but  only  its  fluctua- 
tions. Hence  many  writers  have  supposed  that  the  struggle 
for  existence  belongs  to  animals  and  plants  and  tliat  man  is 
or  should  be  exempt  from  it.  Competition  has  been  idontilied 
with  injustice,  fraud,  or  trickery,  and  it  has  been  supposed  that 
it  could  be  abolished  by  acts  of  benevolent  legislation.  Hut 
competition  is  inseparable  from  life.  Tlie  struggle  for  existence 
may  be  hidden  in  social  conventions  or  its  effects  more  evenly 
distributed  through  processes  of  mutual  aid,  but  its  necessity  is 
always  present.     Competition  is  the  source  of  all  progress. 

The  first  suggestion  of  the  doctrine  of  natural  selection 
came  to  Darwin  through  the  la^v  of  population  as  stated  by 
Thomas  Malthus.  The  law^  of  Malthus  is  in  substance  as  fol- 
lows: Man  tends  to  increase  by  geometrical  ratio — that  is.  by 
multiplication.     The  increase  of  food  supply  is  by  arithmetical 


68  EVOLUTION   AND  ANIMAL   LIFE 

ratio — that  is,  by  addition ;  therefore,  whatever  may  be  the  ratio 
of  increase,  a  geometrical  progression  will  sooner  or  later  outrun 
an  arithmetical  one.  Hence  sooner  or  later  the  world  must  be 
overstocked,  did  not  vice,  misery,  or  prudence  come  in  as  checks, 
reducing  the  ratio  of  multiplication.  This  law  has  been  criti- 
cised as  a  partial  truth,  so  far  as  man  is  concerned.  This  means 
simply  that  there  are  factors  also  in  evolution  other  than  those 
recognized  by  Malthus.  Nevertheless,  Malthus's  law  is  a  sound 
statement  of  one  great  factor.  And  this  law  is  simply  the  ex- 
pression of  the  struggle  for  existence  as  it  appears  among  men. 

The  doctrine  of  organic  evolution  was  first  placed  on  a  firm 
basis  by  Darwin,  because  Darwin  was  the  first  who  clearly 
defined  the  force  of  natural  selection.  Darwin,  however,  rec- 
ognized other  factors,  known  or  hypothetical,  and  was  inter- 
ested more  in  shovving  the  fact  of  descent  and  one  cause  of 
modification  than  in  insisting  on  the  all-sufFiciency  of  the  cause 
especially  defined  by  himself. 

In  later  times,  Weismann  and  his  followers  have  laid  more 
exclusive  stress  on  natural  selection  and  its  Allmacht  or  ex- 
clusive power  in  bringing  about  organic  evolution.  This  view 
is  known  as  Neo-Darwinism  and  the  school  of  workers  who 
profess  it  as  Neo-Darwinians.  Few  investigators  question 
the  far-reaching  influence  of  natural  selection,  but  there  are 
many  phases  in  organic  evolution  which  cannot  be  ascribed 
to  it.  Hence  the  search  for  other  factors  has  been  assiduously 
prosecuted,  and  doubts  of  Darwinism  have  been  widely  ex- 
pressed; but  this  doubting  has  been  thrown  not  so  much  on 
the  Darwinism  of  Darwin,  nor,  as  a  rule,  on  the  law  of  natural 
selection,  but  rather  on  the  Allmacht  claimed  for  it  by  Weis- 
mann and  his  associates. 

Without  attempting  any  elaborate  discussion  of  questions 
still  far  from  settled  we  may  venture  these  suggestions : 

1.  Given  the  facts  of  individual  variation,  of  inheritance, 
and  some  check  to  freedom  of  migration,  natural  selection  would 
accomplish  some  form  of  organic  evolution;  species  would  be 
formed  by  the  survival  of  the  adapted,  adaptations  would  be 
perpetuated,  and  minor  differences  would  develop  in  time  into 
deep-seated  differences. 

2.  With  natural  selection  alone,  however,  the  actual  facts  in 
organic  evolution  as  we  know  them  would  apparently  not  be 
achieved. 


NATURAL   SELECTION;   SEXUAL  SELECTION  60 

3.  In  other  words,  while  natural  selection  furnishes  the 
motive  force  of  change,  other  influences,  extrinsic  and  intrinsic, 
help  to  direct  the  channels  in  whicli  life  runs.  It  is  necessary  to 
consider  other  causes  for  the  great  body  of  indifferent  characters 
or  traits  not  produced  by  adaptation,  and  ai)parently  not  yield- 
ing either  advantage  or  disadvantage  in  the  struggle  for  life. 

4.  The  formation  of  species  of  animals  and  i)lants  through 
natural  selection  finds  an  analogy  in  the  formation  of  rivers 
through  gravitation.  Gravitation  is  the  motive  power  carrying 
the  waters  from  the  uplands  to  the  sea.  The  courses  of  streams 
are  determined  by  a  number  of  minor  influences  acting  in  con- 
currence with  gravitation,  the  final  result  far  more  complex  than 
the  single  cause  would  produce. 

5.  In  like  fashion,  while  natural  selection  is  the  motive 
element  in  descent  or  evolution,  the  total  result  is  due  to  a 
concurrence  of  causes,  and  is  too  complex  to  be  explained  by 
natural  selection,  by  the  principle  of  utility,  or  the  survival  of 
the  fittest  alone,  and  the  varying  effects  must  be  ascribed  to  a 
variety  of  causes. 

Certain  minor  traits,  as  color  patterns,  relative  proportions 
of  parts,  survive — apparently  without  special  utility,  but  because 
these  traits  were  borne  by  some  ancestors  or  group  of  ancestors. 
This  has  been  called  the  Survival  of  the  Existing.  In  making 
up  the  fauna  or  flora  of  any  region  those  organisms  actually 
present  when  the  region  is  first  stocked  must  leave  their  qual- 
ities as  an  inheritance.  If  they  cannot  maintain  themselves 
their  breed  disappears.  If  they  maintain  themselves  in  iso- 
lation their  characters  remain  as  those  of  a  new  species.  In 
hosts  of  cases,  the  survival  of  characters  rests  not  on  any 
special  usefulness  or  fitness,  but  on  the  fact  that  individuals 
possessing  these  characters  have  inhabited  or  invaded  a  certain 
area.  The  princi})le  of  utility  explains  survivals  among  com- 
peting structures.  It  rarely  accounts  for  qualities  associated 
with  geographic  distribution.  The  nature  of  the  animals  which 
first  colonize  a  district  must  determine  what  the  future  fauna 
shall  be.  From  their  actual  s]:)ecific  characters,  largely  traits 
neither  useful  nor  harmful,  will  be  derived  for  the  most  part 
the  specific  characters  of  tlicir  successors. 

It  is  not  essential  to  the  meadow  lark  that  he  should  have 
a  black  blotch  on  the  breast  or  the  outer  tail  feathers  white. 
Yet  all  meadow  larks  have  these  marks,  as  all  shore  larks  possess 

a 


70  EVOLUTION  AND  ANIMAL  LIFE 

the  tiny  plume  behind  the  ear.  Any  character  of  the  parent 
stock,  which  may  prove  harmful  under  new  relations,  will  be 
eliminated  by  natural  selection.  Those  especially  helpful  will 
be  intensified  and  modified.  But  the  great  body  of  characters, 
the  marks  by  wiiich  we  know  the  species,  will  be  neither  helpful 
nor  hurtful.  These  will  be  meaningless  streaks  and  spots, 
variations  in  size  of  parts,  peculiar  relations  of  scales  or  hair  or 
feathers,  httle  matters  which  can  neither  help  nor  hurt,  but 
which  have  all  the  persistence  heredity  can  give. 

In  regard  to  natural  selection  oiu*  knowledge  seems  positive. 
In  regard  to  most  other  factors  of  organic  evolution  we  have 
to  deal  so  far  not  with  clearly  demonstrated  facts  but  with 
"probabilities  of  a  higher  or  lower  order,^'  their  value  to  be 
ultimately  shown  by  experiment. 

In  this  connection  the  following  words  of  Dr.  Edwin  Grant 
Conklin  are  very  pertinent : 

"On  the  whole,  then,  I  believe  the  facts  which  are  at  present  at  our 
disposal  justify  a  return  to  the  position  of  Darwin.  Neither  Weis- 
mannism  nor  Lamarckism  alone  can  explain  the  causes  of  evolution. 
But  Darwinism  can  explain  those  causes.  Darwin  endeavored  to  show 
that  variations,  perhaps  even  adaptations,  were  the  result  of  extrinsic 
factors  acting  upon  the  organism,  and  that  these  variations  or  adap- 
tations were  increased  and  improved  by  natural  selection.  This  is,  I 
believe,  the  only  ground  which  is  at  present  tenable,  and  it  is  but 
another  testimony  to  the  greatness  of  that  man  of  men  that,  after 
exploring  for  a  score  of  years  all  the  ins  and  outs  of  pure  selection  and 
pure  adaptation,  men  are  now  coming  back  to  the  position  outlined 
and  unswervingly  maintained  by  him." 

Finally  we  ought  not  to  suppose  that  we  have  already 
reached  a  satisfactory  solution  of  the  evolution  problem,  or 
are,  indeed,  near  such  a  solution. 

"We  must  not  conceal  from  ourselves  the  fact,"  says  Roux,  "that 
the  causal  investigation  of  organisms  is  one  of  the  most  difficult,  if 
not  the  most  difficult,  problems  which  the  human  intellect  has  at- 
tempted to  solve,  and  that  this  investigation,  like  every  causal 
science,  can  never  reach  completeness,  since  every  new  cause  ascer- 
tained only  gives  rise  to  fresh  questions  concerning  the  cause  of  this 
cause." 


NATURAL   SELECTIOy;   SEXUAL   SELECTION 


71 


In  order  to  explain  certain  important  plicnomena  outside 
the  apparent  range  of  natural  selection,  a  tlieory  of  another  sort 
of  selective  activity  is  recognized  by  many  l^iologists.  Tliis  is 
the  theory  of  Sexual  Selection  first  propounded  by  Darwin. 


Fig.  40. — Male  and  female  humming  bird;  showing  sex  dimorphism,     (.\fter  GouKl.) 


DifTerences  between  male  and  female  individuals  of  tlie  same 
species  are  the  rule  rather  than  tlie  exception  (Fig.  40).  Many 
of  these  differences  are  wliat  miglit  be  called  tlie  necessary  ones 
due  to  the  particular  functions  assumed  hy  eacli  individual  in  this 
differentiation  of  sex.  Of  this  nature  are,  besides  those  funda- 
mental ones  of  the  primary  reproductive  ones,  such  others  as 


72  EVOLUTION  AND  ANIMAL  LIFE 

those  specially  connected  with  the  care  and  rearing  of  the 
young;  as  the  mamma?  of  female  mammals,  the  brood  pouches 
of  the  female  kangaroos  and  opossums,  etc.  But  a  moment's 
reflection  calls  to  mind  the  existence  of  a  host  of  other  differ- 
ences between  males  and  females  of  the  same  species  which 
plainly  have  no  such  immediate  relation  to  the  distinct  functions 
or  duties  assumed  by  each  in  the  business  of  production  and 
care  of  young.  For  example,  the  long  plume  feathers  of  the 
male  bird  of  paradise,  the  curious  chitinous  horns  of  the  male 
leaf-chafer  beetles  (Fig.  41),  the  brilliant  plumage  of  man}^  male 
birds  as  contrasted  with  the  sober  dress  of  the  females,  and  a 
host  of  other  distinguishing  characteristics  of  the  sexes  in  many 
animal  species.  Now  these  differences  are  all  conveniently 
named  by  the  phrase  "  secondary  sexual  differences,"  and  the 
explanation  of  their  origin  has  come  to  be  one  of  the  most 


Fig.  41. — ^Male  and  female  Scarabeid  beetles,  Phaneus  mexicanus,  showng  sex  dimor- 
phism; the  male  with  prominent  dorsal  horn  on  head.     (From  specimens.) 

puzzhng  of  biological  problems.  The  most  familiar  and,  for 
many  5'ears,  a  widely  accepted  solution  of  this  problem,  is  that 
embraced  in  the  theory  of  sexual  selection  proposed  and  fought 
for  by  Darwin  and  Wallace,  but  later  discarded  by  the  latter 
of  these  great  naturalists. 

Before  taking  up  the  sexual  selection  explanation  of  dis- 
tinguishing sex  characters,  it  is  well  to  pay  a  little  further 
attention  to  the  characters  themselves.  And  for  this  purpose  a 
rough  grouping  or  classification  may  be  attempted. 

The  characters  may  be  of  special  use  to  the  possessor  (male 
or  female)  or  for  the  benefit  of  the  young,  such  as  weapons  of 
offense  and  defense  (antlers  of  male  deer,  stings  of  female  bee 
and  wasp,  tusks  of  male  swine,  etc.),  or  special  organs  for  mat- 
ing (seizing  and  holding  organs  of  certain  male  crabs,  suckerhke 
holding  pads  on  the  feet  of  male  water  beetles  (Fig.  42),  or  special 
locomotory  organs  (presence  of  wings  in  the  male  and  their 


NATURAL  SELECTION;  SEXUAL  SELECTION 


73 


absence  in  the  female  in  numer- 
ous insect  species),  or  special 
sense  organs  (the  much  more 
expanded  antennae  of  male  cccro- 
pia,  promethea,  polypliemus,  and 
other  bombycine  moths,  as  com- 
pared with  those  of  the  female), 
or  special  structures  for  the  care 
of  the  young  (milk  glands  of 
female  mammals,  brood  pouches 
of  female  marsupials,  pits  on  the 
back  of  the  male  of  the  frog  ri]:)a 
(Fig.  43),  for  carrying  the  eggs, 
etc.),  or  recognition  marks  (the 
eye  spots,  collars,  wing  bands, 
tail  blotches,  and  such  other  con- 
spicuous color  spots  and  mark- 
ings possessed  by  the  males  and 
wanting  in  the  females  of  various 
bird  species),  or,  finally,  char- 
acters connected  with  special 
habits  of  one  sex  differing  from 
those  of  the  other  (the  pollen 
baskets  and   wax  plates   of  the 

worker  female  honey  bees,  the  winglessness  of  certain  female 
parasitic  insects,  the  males  being  nonparasitic  and  winged,  etc.). 

-  The  special  characters  may  be 
apparently  for  the  purpose  of  attract- 
ing or  exciting  the  other  sex,  as  the 
brilliant  colors,  markings,  and  other 
ornamentation  of  many  male  birds, 
some  manmials,  and  some  reptiles 
and  very  many  fishes,  and  the  cries 
and  songs,  special  odors,  and  curious 
antics  or  dancing  of  the  males  of 
various  animals  (mammals,  l)irds, 
spiders,  insects,  etc.).  In  many  of 
these  cases  the  special  secondary 
sexual  characters  ai)pear  only  tluring 
the  breeding  Reason;  in  others  they 
are  persistent. 


Fig.  42. — Fore  leg  of  male  water  beetle, 
Dijticus,  showing  special  suckerlike 
expansion  of  the  leg.     (After  Miall.) 


Fig.    43.  —  A    male    frog,     Pipn 
aniericann,  carrying  eggs  in  pits 
(After  Darwin.) 


on  its  back. 


?4  INVOLUTION  AND  ANIMAL  LIFE 

The  characters  may  also  dq  of  the  type  called  reciprocal, 
that  is,  organs  which  exist  in  functional  condition  in  one  sex,  but 
in  the  other  appear  in  rudimentary  and  often  nonfunctional 
forms,  as  the  reduced  horns  of  female  antelopes  and  goats,  the 
undeveloped  stridulating  organs  of  female  crickets  and  katydids, 
small  spurs  on  the  female  pheasant,  reduced  mammae  of  male 
mammals,  undeveloped  mimicry  of  male  butterflies,  etc. 


Fig.  44. — Male  (A)  and  female  (B)  of  the  fly,  Calotarsa  insignia  Aid.,  showing  secondary 
sexual  characteristics  on  the  feet  of  the  male.     (After  Aldrich.) 

Finally  the  characters  may  be  indifferent,  that  is,  without 
any  apparent  utility;  as  the  reduced  wings  of  numerous  female 
insects,  the  rudimentary  alimentary  canal  of  the  male  Rota- 
toria, absence  of  antlers  of  female  deer,  loss  of  wings  in  insect 
females, 'Small  differences  in  size  and  markings  between  males 
and  females,  slight  differences  in  wing  form  in  hummingbirds, 
dragon  flies,  and  butterflies,  differences  in  nmiiber  of  tarsal 
and  antennal  segments  in  insects,  etc. 

The  explanation  of  these  various  differences  between  males 
and  females  plainly  cannot  be  a  single  one.  The  extreme  vari- 
ety of  the  secondary  sexual  differences  of  itself  makes  it  neces- 
sary to  find  more  than  one  explanation  for  their  existence.  To 
take  the  most  obvious  case,  it  is  apparent  that  the  useful 
characters,  such  as  the  fighting  antlers  of  the  male  deer,  can  be 
explained  probably  by  natural  selection.  At  least  these  char- 
acters fall  readily  into  line  with  precisely  that  type  of  useful 
specialization  for  whose  explanation  we  rely  on  natural  selec- 
tion. So  practically  all  those  secondary  sexual  characters  of 
our  first  category,  namely,  those  obviously  useful  to  the  pos- 
sessor or  to  its  young,  sucn  as  organs  of  offense  and  defense, 
brood   pouches,   food-producing   or  gathering   organs,   special 


NATURAL  SELECTION;  SEXUAL  SELECTION 


/o 


means  of  locomotion,  etc.,  may  be  considered  to  offer  no  special 
problem.  Although  indeed  the  reason  why  these  useful  cliar- 
acteristics  should  be  possessed  by  but  one  sex  is  by  no  means 
always,  or  perhaps  even  often,  plain  to  us. 

But  the  real  problem  presented  by  secondary  sexual  cliar- 
acters  is  that  thrust  on  us  by  the  nonuseful  and  even  appar- 
ently disadvantageous  differences.  Wliy  the  male  ])ird  of  para- 
dise should  be  decked  out  in  a  plumage  certain  to  make  it 
a  conspicuous  object  to  every  enemy  it  has,  and  of  a  wciglit  and 
difficulty  of  manipulation  that  must  mean  a  constant  demand 
on  the  strength  and  attention  of  the  bird,  is  a  question  that 
demands  a  special  answer.  In  the  same  case  with  tlie  l)ir(l 
of  paradise  are  the  peacock,  the  gorgeous  male  pheasant  (Fig.  45), 


'/f^;v;» 


Fig.  45. — Male  and  female  argus  pheasant;  the  male  is  showTi  in  characteristic  "courting 
attitude."      (From  Tegetmeier's  "  Pheasants.") 


many  hummingbirds  (Fig.  40),  etc.  Now  to  explain  these  ex- 
traordinary secondary  sexual  difforonces  the  tlicory  of  sexual 
selection  has  been  devised. 

This  theory,  in  few  worch^  is  that  there  is  ])ractically  a 
competition  or  struggle  for  mating,  and  tliat  those  males  are 


76  EVOLUTION   AND  ANIMAL   LIFE 

successful  in  this  struggle  which  are  the  strongest  and  best 
armed  or  equipped  for  battle  among  themselves,  or  which  are 
most  acceptable  by  reason  of  ornament  or  other  attractiveness 
to  the  females.  In  the  former  case  mating  with  a  certain 
female  depends  upon  overcoming  in  fight  the  other  suitors,  the 
female  being  the  passive  reward  of  the  victor ;  in  the  second  case 
the  female  is  presumed  to  exercise  a  choice,  this  choice  depend- 
ing upon  the  attractiveness  of  the  male  (due  to  color,  pattern, 
plumes,  processes,  odor,  song,  etc.).  The  actual  fighting  among 
males,  and  the  winning  of  the  females  by  the  victor  is  an  ob- 
served fact  in  the  life  of  numerous  animal  species.  But  a  spe- 
cial sexual  selection  theory  is  hardly  necessary  to  explain  the 
development  of  the  fighting  equipment,  antlers,  spurs,  claws, 
tusks,  etc.  This  fighting  array  of  the  male  is  simpty  a  special 
phase  of  the  already  recognized  intraspecific  struggle ;  it  is  not  a 
fight  for  room  or  food,  but  for  the  chance  to  mate.  But  this 
chance  often  depends  on  the  issue  of  a  life  and  death  struggle. 
Natural  selection  would  thus  account  for  the  development  of 
the  weapons  for  this  pm^pose. 

For  the  development,  however,  of  such  secondary  sexual 
characters  as  ornament,  whether  of  special  plumage,  color, 
pattern,  or  processes,  and  song,  and  special  odors,  and  "love 
dancing,"  the  natural  selection  theory  can  in  no  way  account; 
the  theory  of  sexual  selection  was  the  logical  and  necessary 
auxiliary  theory,  and  when  first  proposed  it  met  with  quick  and 
wide  acceptance.  Wallace  in  particular  took  up  the  theory  and 
applied  it  to  explain  many  cases  of  remarkable  plumage  and 
pattern  development  among  birds.  Later,  as  he  analyzed  more 
carefully  his  cases,  and  those  proposed  by  others,  he  became 
doubtful,  and  finally  wholly  skeptical  as  to  the  theory. 

The  theory  as  proposed  by  Darwin  was  based  on  the  follow- 
ing general  assumptions,  for  the  proof  of  each  of  which  various 
illustrations  were  adduced.  First,  many  secondary  sexual 
characters  are  not  exphcable  by  natural  selection;  they  are  not 
useful  in  the  struggle  for  life.  Second,  the  males  seek  the 
females  for  the  sake  of  pairing.  Third,  the  males  are  more 
abundant  than  the  females.  Fourth,  in  many  cases  there  is  a 
struggle  among  the  males  for  the  possession  of  the  females. 
Fifth,  in  many  other  cases  the  females  choose,  in  general,  those 
males  specially  distinguished  by  more  brilliant  colors,  more 
conspicuous  ornaments,  or  other  attractive  characters.    Sixth, 


NATURAL   SELECTION;   SEXUAL  SELECTION  77 

many  males  sing,  or  dance,  or  otlierwise  draw  to  themselves 
the  attention  of  the  females.  Seventh,  the  secondary  sexual 
characters  are  especially  variable.  Darwin  believed  that  he 
had  observed  certain  other  conditions  to  exist  which  helped 
make  the  sexual  selection  theory  probable,  but  the  conditions 
noted  are  sufficient  if  they  are  real. 

Exposed  to  careful  scrutiny  and  criticism,  the  theory  of 
sexual  selection  has  been  relieved  of  all  necessity  of  explaining 
any  but  two  categories  of  secondary  sexual  characters;  namely, 
the  special  weapons  borne  by  males,  and  special  ornaments  and 
excitatory  organs  of  the  males  and  females.  For  examination 
has  disclosed  the  fact  that  males  are  not  alone  in  the  possession 
of  special  characters  of  attraction  or  excitation.  Regarding 
these  two  categories  Plate  in  his  able  recent  defense  of  Darwinism, 
says  "the  first  part  of  this  theory,  the  origin  of  the  special 
defensive  and  offensive  weapons  of  males  through  sexual  selec- 
tioji,  is  nearly  universally  accepted.  The  second  part  of  the 
theory,  the  origin  of  exciting  organs,  has  given  rise  to  much 
controversy.  Undoubtedly  the  presumption  that  the  females 
compare  the  males  and  then  choose  only  those  which  have  the 
most  attractive  colors,  the  finest  song,  or  the  most  agreeable 
odor,  presents  great  difficulties,  but  it  is  doubtful  if  it  is  possible 
to  replace  this  explanation  by  a  better.''  Some  of  these  diffi- 
culties may  be  briefly  enumerated. 

The  theory  can  be  applied  only  to  species  in  which  the 
males  are  markedly  more  numerous  than  the  females,  or  in  which 
the  males  are  polygamous.  In  other  cases  there  will  be  a  female 
for  each  male  whether  he  be  ornamented  or  not;  and  the  unor- 
namented  males  can  leave  as  many  progeny  as  the  ornamented 
ones,  which  would  prevent  any  accumulation  of  ornamental 
variations  by  selection.  As  a  matter  of  fact,  in  a  majority  of 
animal  species,  especially  of  tlie  higher  vertebrates,  males  and 
females  exist  in  approximately  equal  numbers. 

Observation  shows  that  in  most  species  the  female  is  wholly 
passive  in  the  matter  of  pairing,  accepting  tlie  first  male  that 
offers.  Note  the  cock  and  hens  in  the  barnyard,  or  the  fur  seal 
in  the  rookeries. 

Ornamental  colors  are  as  often  a  characteristic  of  males  of 
kinds  of  animals  in  which  there  is  no  real  pairing,  as  among 
those  which  pair.  How  explain  by  sexual  selection  the  remark- 
able colors  in  the  breeding  season  of  many  fishcS;  in  which  the 


78  EVOLUTION   AND   ANIMAL   LIFE 

female  never,  perhaps,  sees  the  male  which  fertihzes  her  dropped 
eggs?  In  many  fishes  the  spring  ornamentation  of  the  males  is 
just  as  marked  and  just  as  brilliant  as  in  the  birds  or  other 
animals  of  much  higher  intelligence  and  corresponding  power  of 
choice.  Witness  the  horned  dace,  chubs,  and  stone  rollers  in 
any  brook  in  spring. 

Choice  on  a  basis  of  ornament  and  attractiveness  implies  a 
high  degree  of  aesthetic  development  on  the  part  of  the  females 
of  animals  of  whose  development  in  this  line  we  have  no  other 
proof.  Indeed,  this  choice  demands  aesthetic  recognition  among 
animals  to  which  we  distinctly  deny  such  a  development,  as 
the  butterflies  and  other  insects  in  which  secondary  sexual 
characters  of  color,  etc.,  are  abundant  and  conspicuous.  Sim- 
ilarly with  practically  all  invertebrate  animals.  Further,  in 
those  groups  of  higher  animals  where  aesthetic  choice  may  be 
presumed  possible,  we  have  repeated  evidence  that  preferences 
vary  with  individuals.  Certainly  they  do  with  men,  the  animal 
species  in  which  such  preferences  certainly  and  most  conspicu- 
ously exist. 

In  some  human  races  hair  on  the  face  is  thought  beautiful; 
in  others,  ugly.  Besides  even  if  we  may  attribute  fairly  a  cer- 
tain amount  of  aesthetic  feeling  to  such  animals  as  mammals  and 
birds,  is  this  feeling  so  keen  as  to  lead  the  female  to  have 
preference  among  only  slightly  differing  patterns  or  songs? 
Yet  this  assum^ption  is  necessary  if  the  development  of  ornament 
and  other  attracting  and  exciting  organs  is  to  be  explained  by 
the  selection  and  gradual  accumulation  through  generations  of 
slight  fortuitously  appearing  fluctuating  variations  in  the  males. 

There  are  actually  very  few  recorded  cases  in  which  the  ob- 
server believes  that  he  has  noted  an  actual  choice  by  a  female. 
Darwin  records  eight  cases  among  birds.  Since  Darwin,  not 
more  than  half  a  dozen  other  cases,  all  doubtful,  have  been 
noted.  Also  a  few  instances,  all  more  illustrative  of  sexual 
excitation  of  females  resulting  from  the  perception  of  odor  or 
actions,  than  any  degree  of  choice  on  their  part,  have  been 
listed. 

In  numerous  cases  the  so-called  attractive  characters  of  the 
males,  described  usually  from  preserved  (museum)  specimens, 
have  been  found,  in  actual  life,  to  be  of  such  a  character  that 
they  cannot  be  noted  by  the  female.  For  example,  the  brilliant 
colors  and  curious  horns  of  the  males  of  the  dung  beetles  are,  in 


NATURAI.  SELECTION;  SEXUAL  SELECTION  7<) 

life,  always  so  obscured  by  dirt  and  filth  that  there  can  be  no 
question  of  display  to  the  female  eye  about  them.  The  dancing 
swarms  of  many  kinds  of  insects  are  found  to  ])e  comi)osed  of 
males  alone  with  no  females  near  enough  to  see;  it  is  no  case  of 
an  excitatory  flitting  and  whirling  of  many  males  before  the  eyes 
of  the  impressionable  females.  Of  many  male  katydids  singing 
in  the  shrubl^ery  will  not  for  any  female  that  i)articular  song  be 
loudest  and  most  convincing  that  proceeds  from  the  nearest 
male,  not  the  most  expert  or  the  strongest  stridulator?  Simi- 
larly wdth  the  flitting  male  fireflies;  will  not  the  strongest  gleam 
be,  for  any  female,  that  from  the  male  which  happens  to  fly 
nearest  her,  and  not  from  the  distant  male  with  ever  so  much 
better,  stronger  light?  Even  in  the  human  species,  projiin- 
quity  is  recognized  as  the  strongest  factor  in  the  choice  of  mates. 

Several  other  serious  objections  can  also  be  urged  against 
the  sexual  selection  theory,  but  the  most  important  one  of  them 
all  is  that  all  the  evidence  (though  it  is  little  in  quantity  as 
yet,  although  of  good  quality)  based  on  actual  experiment,  is 
strongly  opposed  to  the  validity  of  the  assumption  that  the 
females  make  a  choice  among  the  males  based  on  the  presence 
in  the  males  of  ornament  or  attractive  colors,  pattern,  o:'  special 
structures.  Such  experiments  have  been  undertaken  by  Diiii- 
gen  and  Douglas  with  lizards,  and  by  Mayer  with  moths. 

It  must  be  said,  however,  in  closing  this  brief  discussion 
of  the  sexual  selection  theory,  that  no  replacing  or  substitute 
theory  of  anything  like  tlie  same  plausibility  has  yet  been 
offered  to  take  its  place. 

There  is  no  question  that,  in  many  cases,  brilliancy  of 
breeding  colors,  development  of  processes,  and  the  like,  is 
often  correlated  with  superior  vigor.  This  is  especially  true 
among  fishes  and  birds.  This  reason  could,  however,  not  at 
all  account  for  such  structures  as  the  highly  specialized  stridu- 
lating  organs  of  certain  insects.  The  problem  of  the  secontlary 
sexual  characters,  especially  of  those  which  seem  to  stand  in 
opposition  to  the  natural  selection  theory,  is  one  of  the  most 
pressing  in  present-day  biology. 


CHAPTER  VI 
ARTIFICIAL  SELECTION 

We  can  command  Nature  only  by  obeying  her  laws.  This  prin- 
ciple is  true  even  in  regard  to  the  astonishing  changes  which  are  super- 
induced in  the  qualities  of  certain  animals  and  plants  in  domestication 
and  in  gardens. — Lyell. 

Varieties  are  the  product  of  fixed  laws,  never  of  chance.  With  a 
knowledge  of  these  laws  we  can  improve  the  products  of  nature,  by 
employing  nature's  forces  in  ameliorating  old  or  producing  new  species 
and  varieties  better  adapted  to  our  necessities  and  taptes.  Breeding 
to  a  fixed  line  will  produce  fixed  results.  There  is  no  e\'idence  of 
any  hmit  in  the  production  of  variation  through  artificial  selection; 
especially  if  preceded  by  crossing. — Luther  Burbank. 

The  name  Selection  has  been  long  used  for  the  process  by 
which  breeds  or  races  of  domestic  animals  or  plants  have  been 
formed  in  the  past,  and  for  the  process  by  which  the  skill- 
ful breeder  can  develop  new  forms  at  will.  This  latter  proc- 
ess, called  by  Youatt  "the  magician's  wand,"  by  wdiich  the 
breeder  can  summon  up  any  form  of  animal  which  may  meet 
his  needs  or  please  his  fancy,  has  been  especially  designated  as 
Artificial  Selection.  By  it  we  have  derived  all  of  our  famil- 
iar hosts  of  varieties  of  domesticated  animals  and  plants.  The 
similar  process  in  nature  was  accordingly  designated  by  Darwin, 
Natural  Selection.  It  refers  to  the  development  or  increase 
of  traits  adaptive  or  advantageous  in  the  life  of  a  species, 
through  the  survival  for  reproduction  of  a  greater  proportion  of 
individuals  possessing  the  characters  in  question  than  of  those 
w^hich  do  not.  In  any  race,  it  is  the  individual  w^hich  succeeds 
in  reaching  maturity  which  determines  the  future  of  the  race. 
The  qualities  of  the  multitude  which  die  prematurely  are 
naturally  not  repeated  in  heredity.     In  general,  the  forms  pro- 

80 


ARTIFICIAL  SELECTION 


SI 


duced  in  artificial  selection  are  not  those  which  could  arise 
or  even  exist  in  nature.  In  nature,  hardiness  or  power  of 
resistance  in  competition  or  the  struggle  for  existence  is  all 
important.  In  artificial  selection  stress  is  laid  chiefly  on  char- 
acters useful  or  attractive  to  man.  From  the  standj^oint  of 
self  dependence,  the  improvements  due  to  artificial  selection 
constitute  a  sort  of  retrogression. 

In  general,  the  production  of  a  new  race  of  animals  or  plants 
in  domestication  is  the 
outcome  of  the  work  of 
a  number  of  factors,  in 
which  human  or  artificial 
selection  plays  a  leading 
part,  a  part  which  in- 
creases in  importance 
with  the  degree  of  intel- 
ligent choice  concerned 
in  it. 

In  the  formation  of 
a  new  race  of  animals  or 
plants,  we  may  have  the 
following  stages  or  fact- 
ors: 

1.  Unconscious  se- 
lection with  more  or  less 
complete  isolation. 

2.  Conscious  selec- 
tion of  the  most  desira- 
ble individuals. 

3.  Conscious  selec- 
tion directed  toward 
definite  or  special  ends. 

4.  Crossing  with  other  races  or  with  other  species  (known 
as  hybridizing),  in  order  to  increase  the  range  of  variation,  or 
to  add  or  combine  certain  specific  desirable  qualities  or  to  elimi- 
nate those  undesirable,  this  accompanied  by  conscious  selection 
directed  toward  definite  ends.  On  this  series  of  processes 
breeding  as  a  fine  art  must  depend. 

Taking  as  an  illustration  some  of  the  breeds  of  medium 
wool  sheep  found  in  Southern  England:  we  have  (1)  the  domes- 
tication of  sheep  in  each  of  the  different  counties  or  natural 


Fig.  46. — ^White-crested  black  Polish  cock. 
(After  photograph.) 


82 


EVOLUTION    AND   ANIMAL   LIFE 


areas.  In  tbo  beginning  men  are  satisfied  with  sheep  as  sheep. 
Little  attention  is  paid  to  tlie  distinction  among  individuals. 
Those  which  are  feeble,  ill  nourished,  untamable,  scant-fleeced, 
or  otherwise  unfit  will  be  eliminated,  a  process  which  will  tend 
to  improve  the  stock,  without  giving  the  race  distinctive  quali- 
ties, except  as  compared  with  the  wild  original.  To  form  dis- 
tinct races,  the  factor  of  isolation  must  enter.  Those  in  one 
county,   for   example,    will   be,   at   the   beginning,   somewhat 

different  from  those  in  an- 
other. Each  herd  will  show 
its  own  traits  in  time,  these 
due  primarily  to  differences 
in  the  original  stock, 
secondarily  to  the  pre- 
dominance of  one  form  of 
variation  over  others.  Ex- 
changes of  sheep  will,  by 
cross-breeding,  tend  to 
unify  the  type  of  sheep  in 
some  one  county,  or  on 
some  side  of  a  barrier  across 
which  sheep  are  not  driven. 
With  this,  there  will  be  also 
variations  in  the  character 
of  the  unconscious  selec- 
tion. One  type  of  sheep 
will  flourish  in  a  meadow 
county,  another  on  a  moor, 
and  still  another  on  the 
rocky  hills.  At  any  rate, 
•  as  the  environment  varies, 
so  will  the  character  of  the 
selection.  Thus  as  a  final  result,  in  Southern  England,  the 
Southdown  sheep  of  Sussex  have  tawny  faces  and  legs;  the 
sheep  of  Hampshire  have  black  faces,  ears,  and  legs,  with  a 
black  spot  under  the  tail;  this  black  spot  is  lacking  in  the  sheep 
of  Devon.  In  the  Cheviot  sheep  the  face  and  ears  are  white,  the 
head  free  from  wool,  while  the  ears,  unlike  those  of  most  of  the 
others,  stand  erect.  In  the  dun-faced  Shropshire  sheep,  the 
faces  are  more  or  less  covered  by  wool.  All  these  are  hornless, 
while  the  more  primitive  Dorset  sheep  with  white  face  and  ears 


Fig.  47. — Silver-laced  Wyandotte  cockerel. 
(After  photograph.) 


ARTIFICIAL  SELECTIOX 


83 


have  almost  always  small  curved  horns  which  are  white,  not 
black,  as  in  the  still  more  primitive  Irish  breed.  Most  of  tliese 
distinctive  traits  offer  neither  advantages  nor  disadvantages 
either  to  the  sheep  or  its  owner.      They  are  nonadaptive  or 


m!f?^<rs — rr"  r^ 


if-- 


/,-„.». 


Fig.  48. — ^Typical  Dorset  ewe,  horned.     (After  Shaw.) 


.    '  M  i-^      f/     h".i  ^  I    [  IkA 


--^•••••'§//'/.,...W 


Fig.  49. — Polled  Welsh  sheep,  a  primitive  type,  lean  and  scant  wooled.    (After  Youatt.) 

indifferent  characters.  These  characters  are  therefore  asso- 
ciated with  the  hereditary  traits  of  the  original  stock.  They 
are  preserved  through  segregation  and  they  are  lost  when  herds 
from  different  counties  freely  intermingle.  Free  interbreecHng 
would  give  a  new  and  relatively  uniform  race  of  sheep  over  the 
whole  area  occupied  by  these  separate  breecfs. 


84 


EVOLUTION  AND  ANIMAL  LIFE 


At  this  point  we  may  conceive  that  (2)  conscious  selection  of 
the  more  desirable  individuals  appears.  Through  its  agency, 
Hampshire,  Shropshire,  Cheviot,  and  Southdown  sheep  alike, 
and  the  others  in  their  degree,  tend  toward  larger  size,  more 
wool,  plumper  bodies,  earlier  maturity,  greater  docility,  greater 
fertility,  or  whatever  virtues  the  average  shepherd  may  prize  in 
a  sheep.  While  in  race  traits,  the  breeds  (uncrossed)  tend  to 
diverge  from  one  another,  in  these  adaptive  qualities,  their 
tendency  is  to  run  parallel — or  even  to  converge  toward  greater 
resemblance. 

With  conscious  selection  (3),  there  is  first  a  tendency  to 
emphasize  the  qualities  of  desirable  breeds.     If,  for  example, 


.^rr^ry^--^^. 


'<_ 


Y: 


ii>- 


[I 


|//M'I 


U^ 


.^/'^:>- 


M//^, 


'^P'^Wi}^ 


Fig.  50. — ^Typical  Southdown  ewe.     (After  Shaw.) 

the  Hampshire  is  a  favorite  breed,  the  individuals  showing  most 
distinctly  black  ears,  legs,  and  face  will  be  preferred  by  breeders 
to  those  having  these  parts  pale.  Again,  new  points  of  special 
excellence  will  appear  in  the  breed  and  these  will  be  deliberately 
emphasized,  and  perhaps  by  continuous  selection  a  new  breed 
will  be  formed  having  one  or  more  of  these  as  a  distinctive  trait. 
According  to  Somerville,  one  may  chalk  out  on  a  wall  any 
form  or  type  of  sheep  he  may  like,  and  then  in  time  reproduce 
it  through  selective  breeding. 

In  Nova  Scotia,  Mr.  A.  Graham  Bell  has  developed  a  new 
breed  of  sheep  by  selection,  its  distinctive  character  being  in  the 
increased  milk  flow,  with  an  increased  number  of  teats. 


ARTIFICIAL  SELECTION 


85 


At  Chillenham,  in  England,  is  still  preserved  a  herd  of  the 
original  wild  white  English  cattle,  from  wliich  most  or  all  of  the 
British  breeds  are  said  to  be  descended.  It  is  stated  that  Lord 
Cawdor  has  offered  to  reproduce  this  herd,  by  selection  alone,  in 
three  or  four  generations,  using  the  relatively  primitive  Welsh 
cattle  as  his  base  of  operations. 

In  general,  those  characters  which  are  usually  affected  by 
selection,  whether  natural  or  artificial,  are  characters  of  degree. 
They  are  matters  of  more  or  less,  a  greater  or  less  degree  of 
strength,  swiftness,  size,  endurance,  fertility,  capacity  to  lay 


Fig.  51. — Typical  American  merino  ewe,  a  highly  specialized  breed  with  fine  close-set 

wool.     (After  Shaw.) 


on  fat,  docility,  intelligence,  or  of  whatever  it  may  be.  Under 
ordinary  conditions  these  characters  selected  are  not  traits  of 
Ciuality.  They  do  not  represent  a  new  thing,  a  new  acquisition, 
Init  a  different  degree  of  development  of  an  old  one,  or,  at  most, 
a  change  in  their  relative  arrangement,  an  alteration  of  bio- 
logical perspective. 

The  characters  which  distinguish  true  breeds  as  well  as  true 
species  are  not  of  this  order.  They  are  in  their  essence  quaH- 
tative  and  not  quantitative.  They  are  not,  as  a  rule,  adaptive. 
One  set  of  species  or  race  traits  is  as  good  as  anotlier,  if  the  good 
quahties  or  adaptive  quaUties  are  represented  in  an  equally 
7 


Fig.  52. — Heads  of  various  British  breeds  of  domestic  cattle,  showing  variations  u 
shape  of  head  and  condition  of  horns.     (After  Romanes.) 


FlO.  53.~-Vario\j3  races  of  pigeons,  all  probably  descended  from  the  European  rock 

dove,  CQlumbQ  liviQ,    (After  Haeckpl.) 


88 


EVOLUTION  AND  ANIMAL  LIFE 


high  degree.  The  Southdown  sheep  are  vakied — not  for  their 
Southdown  traits,  but  for  the  excellence  of  their  mutton,  a 
trait  with  which  middle  length  of  wool,  tawny  legs,  naked  faces, 
drooping  ears,  and  absence  of  horns  have  nothing  necessarily  to 
do.     We  value  these  race  traits  only  for  the  other  qualities 


Fig.  54. — Skulls  (in  longitudinal  section)  of  two  breeds  of  domestic  fowl,  shov.ing  the 
large  modification  in  the  cranium:  upper  figure,  Polish  cock;  lower  figure,  Cochin 
cock.     (After  Darwin.) 

which  have  been  in  a  high  degree  associated  with  them  in  the 
heredity  of  the  race. 

Under  crossing  and  selection,  much  bolder  attempts  are 
possible.  When  parents  widely  divergent  are  crossed,  man}^ 
very  different  results  are  attained.  In  general  the  progeny,  at 
least  after  the  first  generation,  diverge  very  widely  from  one 
another.  Some  will  have  the  good  traits  of  both  parent  stocks; 
some  will  have  the  undesirable  ones;  some  will  show  a  mosaic  of 
parental  characters;  some  a  more  or  less  perfect  blend  of  char- 
acters, this  blend  being  definable  as  a  finer  type  of  mosaic. 
Some  will  diverge  widely  from  either  stock,  often  showing  traits 
either  remotely  ancestral  or  wholly  new.  From  desirable  vari- 
ations of  this  sort  new  races  may  be  developed,  each  succeeding 
generation  tending  to  give  greater  fixit}^ 

In  general,  wide  crosses  or  hybrids  are  more  successful  with 
plants  than  with  animals,  because    the    mutual    adjustment 


AKTIFICIAL  SiELECTIOX 


89 


traits  become  more  important  in  the  more  lu^l^ly  specialized 
organisms.  Among  animals,  related  species  often  cannot  be 
crossed  at  all;  the  germ  cells  refuse  to  intermingle.  Sometimes 
there  is  a  very  imperfect  mingling  and  the  resultant  animal  is 
divided  within  itself  and  does  not  live  long.  An  example  of  this 
is  seen  in  Dr.  Mocnkhaus's  cross  of  the  silverside  (Mcnidui) 
with  the  killifish  (Fimdulus).  The  unmixed  chromosomes  of  the 
germ-cell  nucleus  are  seen  unblended,  through  several  segmen- 
tations of  the  egg. 

In  the  case  of  the  mule,  the  cross  of  the  horse  with  the  ass, 
the  hybridization  is  readily  effected,  but  the  resultant  offspring 
is  sterile.     Presumably  the  hereditary  difference  in  the  repro- 


Fig.  55. — Wild  boar  contrasted  with  modern  domestic  pig.      (After  Romanes.) 


ductive  organs  in  the  two  parental  strains  is  too  great  to  allow 
the  normal  development  of  generative  organs  in  the  progeny. 

In  general,  crosses  between  closely  related  species  are  fertile, 
the  degree  of  fertility  being  less  as  ihe  parent  species  are  more 
widely  differentiated.     Among  animals,   any  great   difference 


90  EVOLUTION  AND  ANIMAL  LIFE 

between  the  parent  stocks  renders  hybridisation  impossible. 
But  among  plants,  when  hybrids  are  actually  formed,  fertility 
rather  than  sterility  may  be  taken  as  the  rule.  This  is  the  case 
with  Mr.  Luther  Burbank's  Primus  berry,  a  cross  between  the 
Siberian  raspberry  {Rubus  cratcegifolius)  and  the  Calif  ornian  dew- 
berry or  blackberry  (Rubus  iir sinus).  In  this  form  the  fruit 
excels  in  size  and  abundance  either  parent,  and  the  hybrid 
breeds  true  from  the  seed,  and  ripens  before  either  parent  begins 
to  bloom.  It  was  fixed  in  the  first  generation,  being  in  this  re- 
gard a  rare  exception  to  the  general  rule  of  the  aberration  of 
hybrids.  In  this  and  in  other  respects  the  Primus,  known  to 
be  an  intentional  cross  of  two  species,  behaves  as  though  it 
were  a  distinct  species.  In  like  fashion,  the  Logan  berry,  the 
product  of  an  accidental  cross  at  Santa  Cruz,  in  California,  of 
the  European  raspberr}^  with  the  native  dewberry,  behaves  also 
like  a  distinct  species,  and  is  also  much  su^oerior  in  productive- 
ness to  either  parent. 

The  fine  art  of  the  horticulturist  is  seen  in  the  selection  arid 
fixing  of  the  variations  produced  by  crossing  and  hybridization. 
While  most  of  the  forms  thus  obtained  are  worthless,  a  few 
will  show  decided  advances.  Often  as  much  progress  may  be 
made  in  a  single  successful  cross  or  hybi-idization  as  in  a  dozen 
or  even  a  hundred  generations  of  pure  selection. 

By  selection  alone,  however,  important  results  may  be 
obtained,  with  time  and  patience.  Given  a  variation  in  a  de- 
sired direction  there  is  perhaps  no  actual  limit  bounding  the 
possibilities  of  selection  unless  arising  through  external  or  me- 
chanical conditions.  Thus  selection  for  speed  of  horses  is  limited 
by  the  strength  of  the  material  of  which  a  horse's  leg  is  com- 
posed. The  increase  in  the  number  of  petals  may  be  limited 
by  the  space  on  which  petals  can  stand,  and  the  number  of 
leaflets  in  a  leaf  by  the  length  of  the  rhachis.  Still  there  are 
known  cases  in  which  a  positive  limit  has  been  reached  in  at- 
tempting to  modify  organisms  by  selection  alone. 

Accidental  crossing  within  a  species  may  form  a  useful  basis 
for  selection.  Thus  from  the  seeds  in  a  single  potato  ball  of  the 
Early  Rose  variety,  crossed  by  insects  with  an  unknown  parent, 
]\Ir.  Luther  Burbank  reared  potatoes  of  many  different  sorts: 
red  potatoes,  white  potatoes,  elongate  potatoes,  potatoes  rela- 
tively smooth  and  potatoes  all  eyes  and  "eyebrows.''  Among 
all  these;  one  form^  long,  white^  smooth,  and  mealy,  seemed  far 


ARTIFICIAL  SELECTION 


91 


superior  to  the  others.  From  the  subdivision  of  the  tul^ers  of 
this  seedUng  arose  the  Burbank  potato,  the  most  vahiable 
variety  in  its  economic  relations  now  cultivated  in  America. 
But  with  the  choice  of  this  form  for  preservation,  selection 
ceased,  as  all  plants  of  the  Burbank  potato  in  cultivation  are 


k 


i 


Fig.  56. — Pleads  of  timothy,  showing  improvement  by  selection. 

(After  Hays.) 


subdivisions  of  a  single  original  plant.     New  forms  would  come 
from  further  selection  of  the  Burbank  potato  seed. 

As  illustrations  of  the  more  complex  art  of  hybridization  and 
selection,  we  give  in  the  following  paragraphs  a  brief  account  of 
the  work  of  Luther  Burbank,  the  most  ingenious  and  successful 
of  all  recent  experimenters  in  plant  breeding. 


92 


EVOLUTION   AND   ANIMAL   LIFE 


Burbank  has  originated  and  introduced  a  remarkable  series 
of  plums  and  prunes.  No  less  than  twenty  varieties  are  included 
in  his  list  of  offerings,  and  some  of  them,  notably  the  Gold, 


Fig.  57. — Four  types  of  plumcot:  colors,  red  and  yellow  of  various  shades.     (Photo- 
graph by  Burbank;  about  one-half  diameter.) 

Wickson,  Apple,  October  Purple,  Chalco,  American,  and  Climax 
plums  and  the  Splendor  and  Sugar  prunes,  are  among  the  best 
known  and  most  successful  kinds  now  grown.  In  addition,  he 
is  now  perfecting  a  stoneless  plum,  and  has  created  the  inter- 


FiG.  58. — Seedlings  from  one  hybrid  plum.     (After  photograph  by  Burbank.) 

esting  plumcot  b}^  hybridizing  the  Japanese  plum  and  the 
apricot.  The  plumcot,  however,  has  not  yet  become  a  fixed 
variety  and  may  never  be,  as  it  tends  to  revert  to  the  plum. 


ARTIFICIAL   SELECTION 


93 


The  stoneless  and  seedless  piiim  is  being  produced  by 
selection  from  the  crossing  of  the  descendants  of  a  single  fruit 
in  a  small  wild  plum  with  only  part  of  a  stone  with  the  French 
prune;  the  percentage  of  stoneless  fruits  is  gradually  increasing 
with  succeeding  generations.  The  sugar  prune,  which  promises 
to  supplant  the  French  prune  in  California,  is  a  selected  product 
of  a  second  or  third  generation  variety  of  the  Petit  d'Agen,  a 
very  variable  French  prune.  The  Bartlett  plum,  cross  of  the 
bitter  Chinese  simoni  and  the  Delaware,  a  Burbank  liyl)rid,  has 
a  fragrance  and  flavor  extraordinarily  like  that  of  the  Bartlett 
pear.  The  Climax  is  a  cross  of  the  simoni  and  the  Japanese 
triflora.  The  Chinese  simoni 
produces  almost  no  pollen, 
only  a  few  grains  of  it  ever 
having  been  obtained,  but 
these  few  grains  have  en- 
abled Burbank  to  revolu- 
tionize the  whole  plum 
ship})ing  industry.  Most 
of  Burbank's  plums  and 
prunes  are  the  result  of 
multiple  crossings,  in  which 
the  Japanese  Satsuma  has 
played  an  important  part. 
Hundreds  of  thousands  of 
seedlings  have  been  grown 
and  carefully  worked  over 

in  the  twenty  years'  experimenting  with  plums,  and  single 
trees  have  been  made  to  carry  as  many  as  600  var3'ing  seed- 
ling grafts. 

Burbank  has  originated  and  introduced  the  Yan  Deman, 
Santa  Rosa,  Alpha,  Pineapple  "No.  80,"  the  flowering  Dazzle, 
and  other  quinces;  the  Opulent  peach,  cross  bred  from  the  Muir 
and  Wager;  the  Winterstein  apple,  a  seedling  variety  of  the 
Gravenstein;  and  has  made  interesting,  although  not  profitable, 
crosses  of  the  peach  and  nectarine,  peach  and  almond,  and  plum 
and  almond. 

Next  in  extent,  probably,  to  his  work  with  plums  is  his  long 
and  successful  experimentation  with  berries.  Tliis  work  has 
extended  through  twenty-five  years  of  constant  attention,  has 
involved  the  use  of  forty  different  species  of  Rubus,  and  has 


Fig.  59. — The  larger  plum  is  the  direct  seed- 
ling of  the  smaller,  produced  by  crossing 
the  trifolia/n  (Japan)  plum  and  the  little 
maritima  (Atlantic  Coast)  plum.  (After 
photograph  by  Burbank.) 


94 


EVOLUTION   AND  ANIMAL  LIFE 


resulted  in  the  origination  and  introduction  of  a  score  of  new 
commercial  varieties,  mostly  obtained  through  various  hybridi- 
zations of  dewberries,  blackberries,  and  raspberries. 


;    '^Lti 


I- 


if. 


a: 


-V 


w^^M 


w 


Fig.  60. — Seedlings  of  one  kind  of  hybrid  plum:  colors  almost  black,  deep  crimson, 
light  crimson,  scarlet,  deep  yellow,  and  shades  of  orange  and  yellow,  green  striped, 
spotted  and  speckled;  long  and  short  stems;  sweet,  sour,  bitter,  good,  bad,  and 
indifferent,  firm  and  .soft;  flesh,  yellow,  white;  pink,  red,  crim.son,  striped,  and 
shaded;  stones  of  vanous  shapes  and  sizes,  large,  small,  oval,  round,  of  different 
colors,  some  clingstones,  some  freestones;  foliage  varying  as  much  as  the  rest,  and 
growth  from  short  and  stalky  and  dwarf  to  rampant  exuberance.  (.Photograph  by 
Burbpnk,  ^bout  on^-qu^rter  diameter.) 


Artificial  selection 


05 


Among  tliese  may  especially  be  mentioned  besides  the 
Primus  already  spoken  of,  the  Iceberg,  a  cross-bred  white 
blackberry  derived  from  a  hybridization  of  the  Crystal  White 
(pistillate  parent)  with  the  Lawton   (staminate  parent),  with 


Fig.  G1. — Seedlings  of  the  Japanese  quince,  Pi/riis  Japoiiiar.    colors,  orange   yellow,  or 
ilmost  white,  with  cnmsou  dots  and  spla-shes.     (From  i)hotograph  l<y  Burbauk  ) 


96 


EVOLUTION  AND  ANIMAL  LIFE 


beautiful  snowy-white  berries  so  nearly  transparent  that  the 
small  seeds  may  be  seen  in  them;  the  Japanese  Golden  May- 
berry,  a  cross  of  the  Japanese  R.  palmatus  (with  small,  tasteless, 
dingy  yellow,  worthless  berries)  and  the  Cuthbert,  the  hybrid 
growing  into  treelike  bushes,  six  to  eight  feet  high,  and  bearing 
great,  sweet,  golden,  semitranslucent  berries  which  ripen  before 
strawberries;  the  Paradox,  an  oval,  light-red  berry,  obtained  in 
the  fourth  generation  from  a  cross  of  Crystal  White  Blackberry 
and  Shaffer ^s  Colossal  Raspberry.  While  most  of  the  plants 
from  this  cross  are  partly  or  wdiolly  barren,  this  particular  out- 
come is  an  unusually  prolific  fruit  producer. 

An  interesting  feature  of  Mr.  Burbank^s  brief  account,  in  his 


Fig.  62. — Three  walnuts:   at  left  Japanese  walnut,   at  right  English  walnut, 
and  in  middle  a  hybrid  of  thes£  two.     (From  photograph  by  Burbank.) 


"New  Creations"  catalogue  of  1894,  of  the  berry  experimenta- 
tion is  a  reproduction  of  a  photograph  showing  "a  sample  pile 
of  brush  12  feet  wide,  14  feet  high,  and  22  feet  long,  containing 
65,000  two-  and  three-year  old  seedling  berry  bushes  (40,000 
Blackberry  X  Raspberry  hybrids  and  25,000  Shaffer  X  Gregg 
hybrids),  all  dug  up  with  their  crop  of  ripening  berries."  The 
photograph  is  introduced  to  give  the  reader  some  idea  of  the 
work  necessary  to  produce  a  satisfactory  new  race  of  berries. 
"Of  the  40,000  Blackberry-Raspberry  hybrids  of  this  kind 
'Paradox'  is  the  only  one  now  in  existence.  From  the  other 
25,000  hybrids  two  dozen  bushes  were  reserved  for  further 
trial." 


ARTIFICIAL  SELECTION 


97 


Leaving  Biirbank's  other  fruit  and  berry  creations  un- 
noticed, we  may  refer  to  his  curious  cross-bred  wahiut  results 
(Fig.  03),  the  most  astonishing  of  which  is  a  liybrid  Ijctween 


H 

1 


Fig.  63. — At  left,  leaf  of  English  walnut,  JiKjlnns  regia;  at  right  California  Mack 
walnut,  Jiujlans  californica;  and  in  the  middle  a  leaf  of  the  hybrid  Paradox,  first 
generation.     (From  photograph  by  Burbank.) 


Juglans  Californica  (staminate  parent)  and  J.  nigra  (])istillate 
parent),  which  grows  with  an  amazing  vigor  and  ra})icHty,  the 
trees  increasing  in  size  at  least  twice  as  fast  as  the  combined 
growth  of  both  parents,  and  the  clean-cut,  glossy,  bright  green 


98 


EVOLUTION  AND  ANIMAL  LIFE 


leaves,  from  two  to  three  feet  long,  having  a  sweet  odor  like  that 
of  apples.  This  hybrid  produces  no  nuts,  but  curiously  enough 
the  result  of  the  reverse  hybridization  (i.  e.,  pollen  from  nigi^a  on 


Fig.  64. — Hybrid  seedling  cactuses,  Opuntia,  after  six  months  growth,  showing  num- 
erous varieties.     (From  photograph  by  Burbank.) 

pistils  of  Californica)  produces  in  abundance  large  nuts  of  a 
quality  superior  to  that  possessed  by  either  parent. 

Of  new  vegetables  Burbank  has  introduced  besides  the  Bur- 
bank  and  several  other  new  potatoes,  new  tomatoes,  squashes, 
asparagus,  etc.  Perhaps  the  most  interesting  of  his  experiments 
in  this  field  is  his  attempt,  apparently  destined  to  be  successful, 
tc  produce  a  spineless  and  spiculeless  and  unusually  nutritious 
cactus  (the  spicules  are  the  minute  spines,  much  more  danger- 
ous and  harder  to  get  rid  of  than  the  conspicuous  long  thornlike 
spines)  edible  for  stock,  and  indeed  for  man.  This  work  is 
chiefly  one  of  pure  selection,  for  the  cross-bred  forms  seem  to 
tend  strongly  to  revert  to  the  ancestral  spiny  condition. 

Among  the  man}^  new  flower  varieties  originated  by  Bur- 
bank may  be  mentioned  the  Peachblow,  Burbank,  Coquito,  and 
Santa  Rosa  roses,  the  Splendor,  Fragrance  (a  fragrant  form), 
and  Dwarf  Snowflake  callas,  the  enormous  Shasta  and  Alaska 


ARTIFICIAL  SELECTION 


00 


daisies,  the  Ostrich  plume,  Wavcrly,  Snowdrift,  and  Doul)l(3 
clematises,  the  Hybrid  Wax  Myrtle,  the  extraordinary  Xico- 
timia,  a  hy])rid  between  a  large,  flowering  Nicotiana  and  a 
Petunia,  several  hybrid  Nicotianas,  a  dozen  new  gladioli  and 
ampelopses,  several  amaryllids,  various  dahlias,  the  Fire  poppy 
(Fig.  65),  (a  brilliant,  flame-colored  variety  obtained  from  a 
cross  of  two  white  forms),  striped  and  carnelian  poppies,  and  a 
blue  Shirley  (obtained  by  selection  from  the  Crimson  field  poppy 
of  Europe),  the  Silver  Line  poppy  (ol)tained  by  selection  from 
an  individual  of  Papaver  umhrosum,  showing  a  streak  of  sih'er 


Fig.  65. — At  left,  leaf  and  flower  of  the  pale  yellow  poppy.  Papnvcr  pUusitm;  at  rijiht 
leaf  and  flower  of  the  snow  white  poppy,  Papaver  somniferum;  and  in  the  middle, 
leaf  and  fire-criin.son  flower  of  the  first  generation  hybrid  of  these  two.  (From 
photograph  by  Burbank.) 

inside)  with  silver  interior  and  crimson  exterior,  and  a  Crimson 
California  poppy  (EschschoUzia),  obtained  by  selection  from  the 
familiar  golden  form. 

Perhaps  his  most  extensive  experimenting  with  flowers  has 


100 


EVOLUTION  AND  ANII^L\L  LIFE 


been  done  in  the  hybridizing  of  hhes,  a  field  in  which  many  plant 
breeders  have  found  great  difficulties.  Using  over  half  a  hun- 
dred varieties  as  basis  of  his  work  Burbank  has  produced  a  mar- 
velous variety  of  new  forms  (Fig.  66).  "Can  my  thoughts  be 
imagined/^  he  saj^s,  in  his  " New  Creations "  of  1893;  "after  so 
many  years  of  patient  care  and  labor  [he  had  been  working  over 
sixteen  years],  as,  walking  among  them  [his  new  hlies]  on  a 
dewy  morning,  I  look  upon  these  new  forms  of  beauty,  on  which 


Fig.  66. — An  improved  seedling  lily  with  two  petals. 

by  Burbank.) 


(From  photograph 


other  eyes  have  never  gazed?  Here  a  plant  six  feet  high  with 
yellow  flowers,  beside  it  one  only  six  inches  high  with  dark 
red  flowers,  and  further  on  one  of  pale  straw,  or  snowy  white, 
or  with  curious  dots  and  shadings:  some  deliciously  fragrant, 


ARTIFICIAL  SELECTIOX 


101 


Others  faintly  so;  some  witli  upright,  otliers  with  nodding 
flowers;  some  with  dark  groen,  woolly  leaves  in  whorls  or  with 
polished  light  green,  lanceliko,  scattered  leaves.' 


Fig.  67. — An  extraordinary  apple,  one-half  being  bright  red  and  sour,  and  the  other 
half  greenish  yellow  and  sweet;  note  in  photograjih  the  sharp  line  of  demarkation 
between  the  different  halves.     (From  photograph  by  Burbank.) 

So  far  no  special  reference  has  been  made  to  the  more 
strictly  scientific  aspects  of  Burbank's  work.  Burlxank  has 
been  primarily  intent  on  the  production  of  new  and  improved 
fruits,  flowers,  vegetables,  and  trees  for  the  immediate  benefit 
of  mankind.  But  where  biological  experimentation  is  V.-eing 
carried  on  so  extensively  it  is  obvious  that  there  musL  be  a 
large  accunmlation  of  data  of  much  scientific  value  in  its  rela- 
tion to  the  great  problems  of  heredity,  variation,  and  species- 
forming.  Burbank^s  experimental  gardens  may  be  looked  on, 
from  the  point  of  view  of  the  biologist  and  evolutionist,  as  a 
great  laljoratory  in  which,  at  present,  masses  of  valualjlc  data 
are,  for  lack  of  time  and  means,  being  let  go  unrecorded. 

Of  Burbank's  own  particular  scientific  beliefs  touching  the 
"grand  problems"  of  heredity  Ave  have  space  to  record  but 
two:  fu'st,  he  is  a  thorougli  believer  in  tlie  inheritance  of  ac- 
quired characters,  thus  differing  strongly  from  the  Weismann 
school  of  evolutionists;  second,  he  believes  in  the  constant 
8 


102 


J: VOLUTION  AND  ANIMAL  LIFE 


mutability  of  species,  and  the  strong  individuality  of  each  plant 
organism,  holding-  tbat  the  apparent  fixity  of  characteristics  is  a 
iDhenon^-^-^^  wholly  dependent  for  its  degree  of  reahty  on  the 


Fig.  C8. — Seedlings  of    the  Williams   early  apple,  showing   all  the  colors  ever  found  iu 

apples.     (From  photograph  by  Burbank.) 

length  of  time  this  characteristic  has  been  ontogenetically  re- 
peated in  the  phjdogeny  of  the  race. 

In   like   fashion   to   this   working   with    plants,   breeds   of 
animals  have  been  estabhshed  by  crossing  and  selection  with  a 


ARTIFICIAL  SELECTION 


103 


view  to  the  preservation  of  the  best  traits  of  both.     In  estab- 
lishing tlie  stock  faun  at  Palo  Alto,  Leland  Stanford  had  the 


Fig.  69. — Improvement  in  geranium:  at  left,  the  original  wild  form,  and  at 
right  the  latest  improved  form.     (From  photograph  by  Burbank.) 

conception  of  strengthening  the  trotting  horse  by  a  cross  with 
the  larger  running  horse  or  thoroughbred.  The  result  was  the 
formation  of  a  peculiar  type  of  horse,  large,  strong,  supple, 


'  ! 

• 

Fig.  70. — Sports  found  among  crossed  amaryllids.  the  size  anci  form  markedly  changed; 
the  flowers  are  three  inches  in  diameter.     (From  photograph  by  Burbank.) 

and  intelligent,  very  clean  of  limb  and  sleek   of   coat.     This 
group  of  horses  held  for  some  years  the  world's  records  for 


1Q4  EVOLUTION   AND   ANIMAL   LIFE 

speed  in  their  various  classes  and  ages,  and  the  experiment 
was  in  the  highest  <iegree  successfuL  In  one  sense  such  at- 
temi^*"'  ''"'^  not  experiments.  The  skillful  breeder  knows  that 
'5ut  of  the  many  combinations  possible  in  crossing,  some  few 
will  fall  in  line  with  Jiis  plans.  He  has  only  to  preserve  these, 
and  to  clinch  them^  by  in-and-in  or  segregated  breeding  to 
bring  about  a  result  he  may  have  deemed  possible  or  desir- 
able. It  is  possible,  by  intentional  selection,  to  turn  a  non- 
essential or  race  character  into  a  selective  or  adaptive  one. 
The  Hampshire  sheep  have  black  ears,  but  by  persistent  se- 
lection the  ears  could  probably  be  made  white.  Probably  also 
the  horns  of  the  Dorsets  could  be  bred  on  Hampshires  by 
making  use  of  possible  occasional  reversions  to  the  horned 
stock.  This  result  could  be  attained  very  rapidty  by  a  cross- 
ing with  Dorset  stock,  but  this  triumph  of  the  breeder's  art 
has  rarely  any  homologue  in  the  wild  state  or  in  the  condition 
of  unconscious  selection. 

When  selection  ceases,  the  adaptive  characters  are  likely  to 
decline  or  disappear.  Under  cessation  of  selection,  called  by 
Weismann  panmixia,  no  premium  is  placed  on  traits  of  excel- 
lence, from  the  human  standpoint,  such  as  long  wool,  plump- 
ness or  S3anmetry  of  form;  and  only  the  purely  vegetative  ad- 
vantages of  the  individual  count.  But  while  the  traits  of 
excellence  disappear,  the  race  traits  or  nonadaptive  characters 
persist  unchanged.  A  herd  of  neglected  Hampshire  sheep  is 
still  a  herd  of  Hampshires.  The  black  face^  earS;  and  legs 
remain  black,  with  no  tendency  to  fade. 

When  the  worst  individuals  are  selected  for  breeding,  we 
have  the  reversal  of  selection.  A  flock  of  Hampshire  culls, 
feeble,  loose- jointed,  scant-wooled,  unsymmetrical,  could  be 
used  in  breeding,  and  the  adaptive  characters  usually  sought 
for  could  be  bred  out  of  them.  But  they  would  still  be  Hamp- 
shires, for  the  hereditary  characters  which  had  persisted  with- 
out the  aid  of  selection  would  persist  after  selection  ceases  or 
even  if  it  is  reversed.  When  these  same  characters  are  made  the 
object  of  selection,  they  are  subject  to  the  same  laws  as  ordinary 
adaptive  characters. 

What  is  true  of  a  breed  of  sheep — a  product  of  geographical 
isolation  with  segregative  breeding — is  true  in  a  general  way  of 
any  w^ild  species  of  animals  or  plants.  Its  adaptive  characters 
are  due  to  natural  selection,     These  change  more  rapidly  than 


ARTIFICIAL  SELECTION  105 

the  nonadaptive  characters,  and  respond  more  readily  to  the 
conditions  of  panmixia  or  of  reversal  of  selection. 

In  matters  of  breeding  we  must  distinguish  between  animals 
actually  best  and  those  potentially  best.  An  animal  is  at  its 
actual  best  when  in  prime  condition,  at  the  prime  of  its  life. 
Another  of  far  finer  heredity,  of  far  stronger  ancestry,  may  be 
at  any  given  time  actually  the  inferior  of  the  first.  It  may  be 
too  old,  too  young,  in  too  poor  condition  to  represent  its  own 
best  status. 

It  is  generally  recognized  that,  for  all  breeding  purposes,  the 
animal  potentially  best  is  superior  to  one  which,  otherwise 
inferior,  may  be  actually  best  at  the  time.  The  tendency  of 
heredity  is  to  repeat  the  traits  of  the  ideal  individuals,  which 
the  parents  ought  to  have  been.  More  exactly,  the  tendency  of 
heredity  is  to  produce  individuals  which,  under  like  conditions 
of  food  and  environment,  would  develop  as  the  parents  have 
developed. 

But  it  is  also  recognized  that  the  actual  physical  condition  of 
the  parent  affects  the  offspring.  A  sick  mother  is  likely  to  bear 
an  enfeeljled  child.  Immature  or  declining  sires  do  not  beget 
offspring  as  strong  as  those  begotten  by  them  when  they  are  in 
perfect  strength  and  health.  In  this  matter,  apparently,  we  have 
to  deal  with  two  different  elements,  as  Weismann  and  others  have 
pointed  out.  The  fu'st  is  true  heredity,  the  quality  of  the  germ  cell, 
which  is  not  affected  by  the  condition  of  the  parent.  Weak  or 
strong,  the  offspring  is  of  the  same  kind  or  type  as  the  parentage. 

The  second  element  has  been  called  Transmission.  Its 
relations  are  with  vegetative  development.  The  embryo  is  ill 
nourished  by  the  sick  mother,  and  it  enters  on  life  with  lowered 
vigor.  The  momentum,  if  w^e  may  use  such  a  figure  of  speech, 
is  reduced  from  the  first,  and  the  lost  vitality  may  never  be 
regained.  The  defects  of  the  male  parent  are  perhaps  of  less 
moment,  but  whatever  their  nature  their  results  would  be  of 
the  same  kind.  They  would  not  enter  into  the  heredity  of  the 
offspring,  but  they  might  play  a  large  part  in  retarding  its 
development.  In  the  category  of  transmission,  not  of  heredity, 
would  belong  the  theme  of  Ibsen's  ''Ghosts"  {Gjengdngerc),  the 
development  of  softening  of  the  brain  in  the  son  of  a  debauchee, 
the  alleged  cause  being  that  the  father '"^  nervous  system  was 
vermoulu  (worm-eaten),  if  we  arc  to  accept  the  ghastly  dramo 
as  an  exposition  of  possible  facts. 


106  EVOLUTION   AND  ANIMAL  LIFE 

The  role  played  by  the  phenomena  of  transmission  as  distin- 
guished from  that  of  heredity  has  never  been  clearly  ascertained. 
Many  eminent  writers  ascribe  to  it  a  large  importance.  It  is 
a  central  element  in  Mr.  Casper  Redfield's  theory  of  heredity, 
and  he  brings  together  a  considerable  array  of  facts  and  statis- 
tics to  justify  his  conclusions.  But  the  value  of  statistics  in 
such  matters  is  easily  exaggerated,  because  of  the  difficulty  in 
ascertaining  the  real  causes  behind  the  phenomena  we  try  to 
record.  It  is  fair  to  say  as  a  broad  proposition  that,  as  a  sound 
mind  requires  a  sound  body,  soundness  both  of  mind  and  body 
are  factors  in  giving  to  offspring  the  best  possible  start  in  life. 
The  heredity  unchanged,  there  is  still  a  great  value  in  vigor  of 
early  development. 

The  relation  of  these  matters  to  the  theory  of  organic  evo- 
lutior  is  mainly  here:  artificial  selection  as  a  process  is  of  the 
same  general  character  as  natural  selection;  both  represent  a 
form  of  isolation  or  segregation,  which  prevents  indiscriminate 
mating^  and  which  holds  certain  groups  of  individuals  as  the 
agents  of  reproduction  of  the  species  wathin  a  given  time  or  in 
a  special  area. 

Artificial  selection  intensifies  useful  or  adaptive  characters, 
using  these  words  in  a  broad  sense.  At  the  same  time,  it  per- 
petuates a  series  of  characters,  in  no  wise  useful,  and  in  no 
fashion  adaptive.  The3e  characters  remain  unchanged  for  long 
periods,  and  hence  have  more  value  in  race  distinction  or  in 
classification  than  the  strictly  adaptive  characters  have.  A 
Southdown  sheep  is  plump  and  fat,  on  the  whole  perhajDS  more 
so  than  any  other  t3q3e  of  sheep.  Nevertheless,  it  is  not  by  its 
plumpness  that  we  know  a  Southdown.  It  is  rather  by  the 
character  of  its  wool,  the  color  of  its  face  and  feet,  the  form  of 
its  head.  So  it  is  with  breeds  and  races  generally.  They  are 
formed  primarily  by  isolation  in  breeding,  the  separation  of  a 
few  from  the  many  by  geographical  or  similar  causes,  by  the 
perpetuation  of  the  traits  of  these  few  (the  "survival  of  the 
existing"),  all  this  being  modified  by  the  new  range  of  natural 
and  artificial  selection  and  the  new  reactions  under  the  varying 
conditions  of  a  new  environment. 

It  interests  us  to  know  that  a  similar  process  takes  place  in 
nature.  Geographical  and  topographical  barriers  are  crossed 
in  migration.  These  isolate  a  portion  of  a  species  under  new 
conditions,   with   new   reactions    to   the   environment,  and    a 


ARTIFICIAL   SELECTION  107 

new  range  of  natural  selection.  Adaptive  characters  change 
rapidly,  and  in  ways  more  or  less  parallel,  with  similar  ahera- 
tions  in  related  species.  Characters  nonadaptive,  often  slight 
in  appearance  and  bearing  no  relation  to  tlie  life  of  the  animal, 
become  slowly  but  surely  fixed  as  characters  of  the  species. 
As  two  closely  allied  breeds  of  animals  are  never  found  in  the 
same  region  luiless  purposely  restrained  from  free  interln-eeding, 
so  two  closely  related  s})ecies  never  develop  in  the  same  breeding 
area.  As  the  nearest  relative  of  some  given  breed  of  domestic 
animals  is  found  in  a  given  region  nearly  related  geographicjdly, 
so  is  the  nearest  relative  to  any  given  wild  species  found,  in 
most  cases,  not  far  away.  It  is  to  be  looked  for  on  the  other 
side  of  some  geographic,  topographic,  or  climatic  barrier.  In 
other  words,  the  interrelation  of» variation,  heredity,  geographic 
isolation  and  environmental  features  generally  seems  to  be  tlie 
same  in  the  formation  of  domestic  races  as  in  tliat  of  t!ie 
formation  of  natural  species.  The  principal  new  element  intro- 
duced in  the  art  of  selective  breeding  is  tliat  of  i)urposoful 
crossing,  the  removal  of  the  barriers  wliich  separate  well- 
differentiated  forms,  for  the  purpose  of  beginning  a  new  series 
to  l)e  selected  toward  a  predetermined  end. 

It  has  been  recently  repeatedly  stated  that  most  races  of 
domesticated  animals  or  plants  find  their  origin  in  a  mutation 
or  saltation  of  some  sort.  In  our  judgment,  there  is  not  sufli- 
cient  evidence  to  prove  tliis  view.  There  are  few  cases  of 
either  races  or  species  known  to  have  originated  in  this  way. 
That  sucli  is  in  fact  the  general  law  of  race  or  species  origin, 
we  see  little  reason  to  believe.  One  of  the  few  well-known 
illustrations  of  race-forming  through  saltation  is  that  of  the 
Ancon  sheep.  In  1791,  in  }Jassachiisetts,  a  ram  was  born  witli 
unusually  short  legs.  As  this  character  was  useful,  preventing 
the  sheep  from  leaping  over  stone  walls,  the  owner  of  this  sheep 
used  the  ram  for  l)reeding  purposes,  and  succeeded  in  isolating 
a  short-legged  strain  of  sheep  known  as  the  Ancon  sheep.  80 
far  as  known  to  us,  this  type  of  sheep  differed  in  this  character 
alone  from  the  common  sheep  of  Connecticut.  With  the  later 
advent  of  the  more  heavy- wooled,  and  therefore  more  profitable, 
Merino,  the  Ancon  sheep  disappeared.  A  recent  similar  case  of 
race  origin  from  a  prepotent  sport  is  that  of  tlu^  i)()ll(^l  llere- 
fords  arising  in  Kansas  from  a  hornless  Hereford  bull. 


CHAPTER  VII 

VARIOUS  THEORIES   OF  SPECIES-FORMING 
AND   DESCENT  CONTROL 

The  four  factors  named,  variation,  inheritance,  selection,  and  sepa- 
ration, must  work  together  in  order  to  form  different  species.  It  is 
impossible  to  tliink  that  one  of  these  should  work  by  itself  or  that 
one  could  be  left  aside. — Ortmann. 

As  mentioned  in  the  introductory  chapter  on  the  factors  of 
evolution  (Chapter  IV) ,  and  as  referred  to  several  times  in  the 
chapter  on  natural  selection,  the  factor  of  the  segregation  or 
isolation  of  groups  of  individuals  must  be  taken  into  account  in 
any  discussion  of  species-forming  causes.  This  factor  has  long 
been  recognized  by  biologists,  that  phase  of  it,  and  undoubtedly 
the  most  important  of  its  several  phases,  called  geographic 
or  topographic  isolation  or  segregation  being  very  clearly 
stated  and  its  importance  emphasized  by  Moritz  Wagner  in 
1868.  Alfred  Russel  Wallace  gave  much  attention,  in  his  years 
of  active  investigation,  to  the  general  subject  of  geographical 
distribution,  and  was  a  pioneer  in  calling  the  attention  of  natu- 
ralists to  the  great  significance,  in  the  light  of  the  evolution 
theory,  of  the  facts  of  the  geographical  distribution  of  both 
animals  and  plants.  To-day,  especially  among  American 
biologists,  the  factor  of  topographic  segregation  is  recognized 
as  one  of  the  most  im])ortant  of  species-molding  influences. 
Indeed  it  seems  self-evident  to  many  naturahsts  that  natural 
selection  is  impotent  as  an  actual  cause  of  species-forming  with- 
out some  effective  sort  of  isolation  factor  to  assist  it.  Because 
of  the  importance  in  the  eyes  of  present-day  naturalists  of  the 
geographic  isolation  factor  we  have  given  (Chapter  VIII),  a 
brief  special  discussion  of  this  factor.  In  addition,  in  Chapter 
XIV,  will  be  found  a  discussion  of  the  more  general  subject 
of  geographical  distribution. 

108 


VARIOUS  THEORIES   OF   SPECIES-FORMING  109 

But  it  is  conceivable  that  isolation  may  be  effected  in  other 
ways  than  by  actual  segregation  or  geographic  separation  of 
individuals.  Anything  that  could  lead  to  exclusive  or  dis- 
criminate breeding  among  certain  individuals  of  a  species  would 
result  in  the  isolation  of  these  individuals  from  the  rest  of  the 
species  as  effectively  as  their  actual  separation  from  others  by 
a  geographic  or  topographic  barrier.  Now  there  are  various 
influences  or  conditions  that  miglit  conceivably  bring  about 
such  a  state  of  affairs,  and  some  of  these  have  been  actually 
observed  to  exist.  It  is  of  interest  to  note  that  this  kind  of 
isolation  differs,  in  a  rather  important  way,  from  purely  geo- 
graphic isolation  in  that  the  latter  is  almost  sure  to  be  wholly 
indiscriminate  as  regards  the  individuals  comprised  in  an  isolated 
group,  whil(^  the  former,  which  has  been  called  physiological 
isolation,  will  be  discriminate.  That  is,  there  will  be  a  struc- 
tural or  physiological  peculiarity  common  to  all  the  "  isolated '' 
individuals,  it  being  by  virtue  of  this  common  peculiarity 
(something  not  common  to  other  individuals  of  the  same 
species)  that  the  isolation  actually  exists. 

Romanes  has  been  the  chief  champion  of  the  physiological 
isolation  factor.  And  we  may  advantageously  refer  directly  to 
his  writings  for  a  specific  statement  of  different  forms  or  phases 
of  this  kind  of  isolation.  In  '^Darwin  and  After  Darwin,''  III, 
p.  7  et  seq.,  he  writes: 

"Now  the  forms  of  discriminate  isolation,  or  homogamy,  are  very 
numerous.  When,  for  example,  any  section  of  a  species  adopts 
somewhat  different  habits  of  life,  or  occupies  a  somewhat  different 
station  in  the  economy  of  nature,  homogamy  arises  within  that  section. 
There  are  forms  of  homogamy  on  which  Darwin  has  laid  great  stress, 
as  we  shall  presently  find.  Again,  when  for  these  or  any  other  reasons 
a  section  of  a  species  becomes  in  any  small  degree  modified  as  to  form 
or  color,  if  the  species  happens  to  be  one  where  any  psychological  pref- 
erence in  pairing  can  be  exercised — as  is  very  generally  the  case  among 
the  higher  animals — exclusive  breeding  is  apt  to  ensue  as  a  result 
of  such  preference;  for  there  is  abundant  evidence  to  show  that,  both 
in  birds  and  mammals,  sexual  selection  is  usually  opjiosed  to  the 
intercrossing  of  dissimilar  varieties.  Once  more,  in  the  case  of  plants, 
intercrossing  of  dissimilar  varieties  may  be  prevented  by  any  slight 
difference  in  their  seasons  of  flowering,  of  topographical  stations,  or 
even,  in  the  case  of  flowers  which  depend  on  insects  for  their  ferti- 


no  EVOLUTION   AND   ANIMAL   LIFE 

ligation,  by  differences  in   the   instincts    and    preferences   of    their 
visitors. 

"But,  without  at  present  going  into  detail  with  regard  to  these 
different  forms  of  discriminate  isolation,  there  are  still  two  others, 
both  of  which  are  of  much  greater  importance  than  any  that  I  have 
hitherto  named.  Indeed,  these  two  forms  are  of  such  immeasurable 
importance  that  were  it  not  for  their  virtually  ubiquitous  operation, 
the  process  of  organic  evolution  could  never  have  begun,  nor,  having 
begun,  continued. 

"The  fh-st  of  these  two  forms  is  sexual  incompatibility — either 
partial  or  absolute — between  different  taxonomic  groups.  If  all  hares 
and  rabbits,  for  example,  were  as  fertile  with  one  another  as  they  are 
within  their  own  respective  species,  there  can  be  no  doubt  that  sooner  or 
later,  and  on  common  areas,  the  two  types  would  fuse  into  one.  And 
similarly,  if  the  bar  of  sterility  could  be  thrown  down  as  between  all 
the  species  of  a  genus,  or  all  the  genera  of  a  family,  not  otherwise  pre- 
vented from  intercrossing,  m  time  all  such  species,  or  all  such  genera, 
would  become  blended  into  a  single  type.  As  a  matter  of  fact,  com- 
plete fertility,  both  of  first  crosses  and  of  their  resulting  hybrids,  is  rare, 
even  as  between  species  of  the  same  genus;  while  as  between  genera  of 
the  same  family  complete  fertility  does  not  appear  ever  to  occur,  and, 
of  course,  the  same  applies  to  all  the  higher  taxonomic  divisions.  On 
the  othei*  hand,  some  degree  of  infertility  is  not  unusual  as  between 
different  varieties  of  the  same  species;  and,  wherever  this  is  the  case, 
it  must  clearly  aid  the  further  differentiation  of  those  varieties.  It 
will  be  my  endeavor  to  show  that  in  this  latter  connection  sexual 
incompatibility  must  be  held  to  have  taken  an  immensely  important 
part  in  the  differentiation  of  varieties  into  species.  But  meanwhile  we 
have  only  to  observe  that  wherever  such  incompatibility  is  concerned, 
it  is  to  be  regarded  as  an  isolating  agency  of  the  very  first  importance. 
And  as  it  is  of  a  character  purely  physiological,  I  have  assigned  to  it 
the  name  Physiological  Isolation;  while  for  the  particular  case  where 
this  general  principle  is  concerned  in  the  origination  of  specific  tj^es, 
I  have  reserved  the  name  Physiological  Selection. 


)} 


If  the  factors  of  variation,  heredity,  natural  selection,  and 
isolation  are,  in  the  minds  of  most  naturalists,  the  chief  factors 
in  species-forming  and  descent  control,  and  a  combination  of 
these  factors  is,  in  the  belief  of  these  same  naturalists — the  so- 
called  selectionists  or  Neo-Darwinians — a  sufficient  causal  ex- 
planation of  organic  evolution,  there  are  many  other  natural- 


VAUIOrS  THEORIES  OF  SPECIES-FORMING  111 

ists  who  have  no  siicli  high  esteem  of  the  vahie  of  natural 
selection.  These  believe,  variously,  that  (a)  to  the  selection 
factors  other  auxiliary  or  helping  ones  are  to  be  added,  or  (6) 
that  various  other  fi'.ctors  are  equally  potent  in  species-forming, 
or  (c)  that  these  other  factors  are  the  more  important  ones,  or 
finally  (d)  that  the  S(;lection  factors  are  of  no  importance  at  all, 
that  is,  have  no  reality.  Before  Darwin,  tlie  French  naturalist 
Lamarck  had  clearly  enunciated  an  explaining  theory  of  species 
transformation,  and  there  are  to-day  many  naturalists  who 
believe  that  the  Lamarckian  explanation,  or  its  fundamental 
assumption,  is  true,  or,  at  least,  that  it  is  based  on  the  more 
important  and  effective  factors  in  evolution.  These  natural- 
ists have  been  called  Neo-Lamarckians.  Some  of  these  have 
formulated  theories  of  their  own  based  on  Lamarckian  funda- 
mentals, but  developed  in  directions  more  or  less  obviously  away 
from  characteristic  Lamarckism. 

Still  other  fundamental  causal  factors  than  the  Darwinian 
ones  of  selection  and  the  Lamarckian  ones  of  accumulated  effect 
of  use,  disuse,  and  functioned  stimulation  are  assumed  in  certain 
other  theories  of  species  cliange  and  general  evolution.  Nageli, 
a  botanist  and  natural  })hilosopher,  believed  in  a  special  inherent 
vitalistic  principle  or  force  in  living  matter  which  tends  to  pro- 
duce progressive  differentiation  and  evolution.  Von  Kolliker, 
Korschinsky,  and  de  Vrics  believe  that  species-forming  occurs 
by  definite  sudden  small  (or  larger)  fixed  changes  or  mutations, 
so  that  for  them  a  mutational  or  discontinuous  variation  is  the 
fundamental  causal  factor  in  species  transformation.  Numerous 
paleontologists  believe  that  variation  follows  determinate  lines 
in  its  occurrence,  so  that  evolution  is  orthogenetic,  with  its  lines 
primarily  fixed  by  determinate  variation. 

We  may  then  examine  briefly  some  of  the  more  important 
special  theories  or  groups  of  theories  put  forward  by  biologists 
either  as  auxiliary  and  subordinate  to  the  more  generally 
known  Darwinian  theory,  or  as  alternative  with  or  substitutes 
for  this  theory. 

First  to  be  mentioned  should  be  the  transmutation  theory 
of  Lamarck.  In  its  simplest  expression  it  is,  that  every  individ- 
ual organism  is,  throughout  its  lifetime,  reacting  to  environ- 
mental stimuli  and  conditions  in  such  ways  as  to  change  its 
structure  and  its  habits  in  greater  or  less  degree  from  the 
structure  and  habits  of  its  parents  and  ancestors,  this  change 


112  EVOLUTION  AND  ANIMAL  LIFE 

coming  about  specifically  from  the  varying  effects  of  use  or 
disuse  of  parts,  and  the  functional  stimulation  of  other  parts 
in  response  to  such  extrinsic  conditions  as  light,  contact,  tem- 
perature, pressure,  color,  etc.,  etc.  The  changes  effected  will, 
in  the  nature  of  things,  be  essentially  adaptive.  Now,  these 
adaptive  changes,  these  variations,  or  new  characters  acquired 
during  the  lifetime  of  the  individual  will  be,  in  Lamarck^s  belief, 
inherited,  if  not  in  full,  at  least  in  partial  degree,  by  the  offspring. 
These  in  turn  submitted  to  similar  or  to  different  environ- 
mental influences  will  continue  the  changes  either  cumulatively 
or  diversely.  By  this  steady  direct  change  and  adaptation  to 
environment  the  species  is  ever  modifying  and  transforming. 
Evolution  marches,  and  marches  adaptively  and  advanta- 
geously. 

But  modem  natiu-alists  find  a  most  unfortunate  impediment 
to  this  simple,  direct,  and  sufficient  explanation  of  species- 
forming  and  evolution  in  the  apparent  untruth  of  the  assumption 
that  the  characters  acquired  by  an  individual  in  its  lifetime  are 
transmitted  by  inheritance  to  its  young.  This  question,  fun- 
darfiental  to  the  Lamar ckian  theor}^,  of  the  inheritance  or  non- 
inheritance  of  acquired  characters  has  long  been  one  of  the  most 
hotly  debated  points  in  evolution  biology.  As  we  have  devoted 
a  number  of  pages  to  its  particular  discussion  in  our  later  chap- 
ter on  heredity  (Chapter  X),  we  need  not  anticipate  that 
discussion  here.  It  is  sufficient  to  say  that  as  far  as  scientific 
proof,  that  is,  evidence  from  actual  observation  and  experiment, 
goes,  those  naturalists  led  by  Weismann,  who  deny  this  inheri- 
tance, have  at  present  distinctly  the  better  of  the  argument. 

The  orthogenetic  evolution  theories  of  various  authors, 
based  upon  the  assumed  occurrence  of  variations  in  determinate 
fines  or  directions  (a  restricted  and  determinate  variation  as 
compared  with  the  nearly  infinite,  fortuitous,  and  indeterminate 
variation  assumed  in  the  selection  theory) ,  are  of  several  types. 
The  mention  of  two  will  reveal  pretty  well  the  more  important 
characters  of  all.  Not  a  few  biologists  have  always  beUeved  in 
the  existence  of  a  soi^t  of  mystic,  special  vitalistic  force  or  prin- 
ciple by  virtue  of  which  determination  and  general  progress  of 
evolution  is  chiefly  fixed.  Such  a  capacity,  inherent  in  living 
matter,  seems  to  include  at  once  possibility  of  specific  adapta- 
tion and  the  possibility  of  progressive  or  truly  evolutionary 
change.     Not  all  evolution  is   in   a  single  direct  line,  to   be 


VARIOUS  THEORIES   OF  SPECIES-FORMING  113 

sure;  ascent  is  not  up  a  single  ladder  or  along  a  single  genealogi- 
cal branch,  but  these  branches  are  few  (as  indeed  we  actually 
know  them  to  be,  however  the  restriction  may  be  brought  about) 
and  the  evolution  is  always  progressive,  that  is,  toward  what  wo, 
from  an  anthropocentric  point  of  view,  are  constrained  to  call 
higher  or  more  ideal  life  stages  and  conditions. 

Other  naturalists  also  seeming  to  see  this  course  of  determin- 
ate or  orthogenetic  evolution,  but  not  inclined  to  surrender  their 
disbelief  in  vitalism,  in  forces  over  and  beyond  the  familiar 
ones  of  the  physicochemicj^l  world,  have  tried  to  adduce  a 
definite  causomechanical  explanation  of  orthogenesis.  The 
best  and  most  comprehensible  types  of  this  explanation  are 
those  essentially  Lamarckian  in  princi])le,  in  which  the  direct  in- 
fluence on  living  matter  of  environmental  conditions,  the  direct 
reactions  of  the  life  stuff  to  stimuli  and  influences  from  the 
world  outside,  are  the  causal  factors  in  such  an  explanation. 
But  while  every  naturalist  will  grant  that  such  factors  do  change 
and  control  in  considerable  degree  the  life  of  the  individual, 
most  see  no  mechanism  or  means  of  extending  this  control 
directly  to  the  species. 

The  stumbling  block  of  heredity,  the  means  and  mode  of 
inheritance,  as  we  so  far  know  them,  are  directly  in  the  wa}^  of 
any  general  acceptance  of  such  a  theory  of  evolution  under  the 
direct  control  of  such  "primary  factors  of  life.^'  Ontogenetic 
species,  that  is,  conditions  of  structure  and  habit  common  to 
many  individuals  of  one  kind,  the  conditions  due  to  sameness 
of  intrinsic  and  extrinsic  factors  in  development,  constitute  a 
category  of  organisms  which  at  any  given  time  and  place  seem 
very  real,  and  are  for  the  moment  truly  real.  But  their 
environment  is  remaining  fairly  constant.  We  speak  easil}'  of 
-the  flux  of  Nature:  her  everchangingness.  And  in  the  large 
we  are  speaking  only  of  the  truth.  But  during  our  brief 
period  of  observation  of  the  few  generations  of  this  or  that  kind 
of  animal  or  plant  that  comes  under  om*  eyes  and  microsco|")es, 
the  nature  environing  these  generations  may  be  nearly  uniform. 
What  are  the  changes  in  the  desert  in  a  score  or  a  hundred  or  a 
thousand  of  years?  What  changes  in  life  conditions  on  the 
barren  storm-swept  peaks  of  the  mountain  ranges?  What  in 
the  waters  of  that  brackish  bay  or  sweet-water  lake  apart  from 
the  paths  of  man?  Ontogenetic  species  have  a  seeming  of 
reality,  but  so  far  as  our  present;  knowledge  goes  it  is  only  a 


114  EVOLUTION   AND   ANIMAL   LIFE 

seeming:  reality  vanislies  with  the  death  of  the  individual: 
their  young  can  perpetuate  their  specific  pecuharities  only  if 
the  environmental  conditions  of  their  development  are  identical 
with  those  wdiich  attended  the  growing  up  of  their  parents. 
Variations  in  this  environment  will  determine  variations  in 
them,  and  their  father's  kind  will  exist  no  more. 

The  authors  of  this  book  beheve  that  more  characters  of 
species  than  are  commonly  thought  are  of  this  shifty,  ephemeral 
character;  that  not  a  few  so-cc^lled  true  species  are  only  onto- 
genetic species  held  for  a  num.ber  of  generations  true  to  a  type 
simply  because  the  environment,  the  extrinsic  factors  in  the 
development  of  all  the  individuals  in  these  successive  genera- 
tions, are  the  same.  But  how  these  individual  characteristics 
and  changes  can  be  put  into  the  heredity  of  the  race  we  do  not 
understand.  "There  is  no  fixity  in  species  other  than  that 
due  to  the  long-repeated  ontogenetic  reiteration  of  this  or  that 
characteristic,''  says  Luther  Burbank.  And  he  speaks  from  the 
conviction  forced  on  him  through  thirty  years  of  the  closest  sort 
of  observation  and  personal  experience  of  the  life  of  plants. 
And  yet,  however  strongly  our  own  minds  respond  to  a  desire 
to  believe  this — it  would  be  so  clarifying — the  obstinate  "no 
mechanism"  objection  stands  boldly  up  to  check  our  sympa- 
thetic reasoning. 

Finally  we  should  refer  to  the  theories  of  heterogenesis  or 
species-forming  by  mutations  or  saltations,  which  have  been 
proposed  at  various  times  as  a  substitute  for  the  theory  of 
species-forming  by  the  gradual  transformation  through  selec- 
tion. During  the  discussion  in  the  first  few  years  after  the 
appearance  of  Darwin's  "Origin  of  Species,"  the  German  zoolo- 
gist von  Kolliker  expressed  the  belief  that  the  change  from 
species  to  species  would  probably  be  found  to  be  more  sudden 
and  more  distinctive  than  Darwin's  theory  permitted  one  to 
assume.  Later,  the  Russian  botanist  Korschinsky,  on  a  basis 
of  general  observation  and  some  not  very  extensive  personal 
experimentation,  definitely  fornmlated  a  theory  of  species- 
forming  by  heterogenesis  which  he  placed  strongly  in  contrast 
with  Darwin's  theory  of  gradual  transformation  by  selection, 
which  later  theor}^  he  claimed  should  be  wholly  given  up.  But 
not  until  the  publication  of  de  Vries's  \A'ork,  Die  Mutations-, 
theorie,  in  which  are  recorded  the  results  of  close  personal 
observation  and  experimentation  for  twenty  years  on  race  and 


VARIOUS  THEORIES   OF  SPECIES-FORi\IIXG  115 

species-forming  in  plants  has  the  theory  of  species-forming  by 
mutations,  or  sudden  fixed  changes  (lesser  or  greater)  had  any 
considerable  adoption  or  even  general  attention. 

At  the  present  moment,  probably  because  of  a  strong  re- 
action against  the  too  blind  acceptance  and  general  over- 
emphasis of  the  selection  doctrines,  and  because,  too,  of  the 
unusually  extensive  character  of  de  Vries's  experimentation  and 
observation,  and  his  trenchant  criticism  of  the  weak  places 
in  the  other  theories,  with  the  generally  weighty  character  of 
his  work  and  reputation,  because  of  all  this  the  theory  of  species- 
forming  by  nuitations  has  at  the  present  moment  a  fairly  large 
l)ody  of  adherents  among  reputable  biologists.  And  yet  the 
actual  evidence  of  tested  observation  on  which  the  theory  rests 
is  curiously  meager.  One  hastens  to  admit,  however,  that 
similar  evidence  for  the  theory  of  direct  species-forming  by 
selection  is  also  meager.  While  apparently  no  one  has  ever 
seen  a  case  of  species-making  by  the  natural  selection  of  slight 
fluctuating  variations,  de  Ynes  seems  to  be  almost  the  only 
one  who  has  observed  actual  cases  of  species-making  by  hetero- 
genesis,  and  he  has  seen  very  fev/.  And  in  the  nature  of  things, 
the  opportunities  for  this  kind  of  evidence,  that  is,  that  of  actual 
observation,  ought  to  be  much  larger  in  the  case  of  hetero- 
genesis  than  in  that  of  general  transformation  by  the  selection 
of  slight  variations.  An  account  of  the  exact  character  of 
the  de  Vriesian  mutations  is  included  in  our  later  chapter  on 
variation  and  mutation.  Our  readers  should  realize,  that 
however  much  tliey  may  see  of  this  theor}^  in  present-da}-" 
popular  scientific  literature,  and  however  strongl}^  the  case 
may  be  put  in  favor  of  the  mutation  theory  cf  species  origin, 
this  theory  is  not  accepted  by  the  great  body  of  biologists  as 
entitled  to  replace  the  Darwinian  theory. 

We  may  close  this  chapter  with  a  reference  to  a  pregnant 
sentence  of  ^he  American  paleontologist,  Osborn,  in  a  lecture 
entitled  The  Unknown  Factors  of  Evolution'^:  "The  general 
conclusion  we  reach  from  a  survey  of  the  whole  field  is  that  for 
Buffon^s  and  Lamarck's  factors  we  have  no  theory  of  heredity, 
while  the  original  Darwinian  factor,  or  Neo-I)arwinism,  offers 
an  inadec^uate  explanation  of  evolution.  If  acquired  varia- 
tions are  transmitted,  there  must  be,  therefore,  some  unknown 
principle  in  heredity;  if  they  are  not  transmitted,  there  must  be 
some  unknown  factor  in  evolution."     Our  present  plight  seemg 


116  EVOLUTION  AND  ANIMAL  LIFE 

to  be  exactly  this-:  we  cannot  explain  to  any  general  satisfac- 
tion species-forming  and  evolution  without  the  help  of  some 
Lamarckian  or  Eimerian  factor;  and  on  the  other  hand,  we 
cannot  assume  the  actuality  of  any  such  factor  in  the  light  of 
our  present  knowledge  of  heredity.  The  discovery  of  the 
"unknown  factors  of  evolution"  should  be  the  chief  goal  of  all 
present-day  biologic  investigation. 


CHAPTER  VIII 

GEOGRAPHIC   ISOLATION   AND   SPECIES- 
FORMING 

"For  me,  it  is  the  chorology  of  organisms,  the  study  of  all  the 
important  phenomena  embraced  in  the  geography  of  animals  and 
plants,  which  is  the  surest  guide  to  the  knowledge  of  the  real  phases  in 
the  process  of  the  formation  of  species." — Moritz  Wagner. 

A  FLOOD  of  light  may  be  thrown  on  the  general  problem 
of  the  origin  of  species  by  the  study  of  certain  evidence  as  to 
the  ^  actual  origin  of  species  with  which  we  may  be  familiar,  or  of 
which  the  actual  history  or  the  actual  ramifications  may  in 
some  degree  be  traced. 

In  such  cases,  one  of  the  first  questions  naturally  asked  's 
this:  Where  did  the  species  come  from?  Migration  form?  a 
large  part  of  the  history  of  any  species  or  group  of  forms.  The 
fauna  of  any  given  region  is  made  up  of  the  various  species  of 
animals  living  naturally  within  its  borders.  The  flora  of  a 
region  is  made  up  of  the  plants  which  grow  naturall}"  within 
its  limits.  Of  all  these,  animals  and  plants,  the  inhabitants 
of  most  regions  are  apparently  largely  migrants  from  some 
other  region.  Some  have  entered  the  region  in  question 
before  acquiring  their  present  specific  characters;  others  come 
after  having  done  so.  W^hich  of  these  conditions  apply  to  an}^ 
given  case  can  sometimes  be  ascertained  by  the  comparison 
of  the  individuals  along  the  supposed  route  of  migration. 

Thus,  Dr.  C.  Hart  Merriam  has  undertaken  to  show  the 
actual  origin  of  nine  species  of  Calif ornian  chipmunks  (Eutamias) 
by  an  elaborate  study  of  their  distribution,  ada})tations,  and 
transformations.     He  finds  them  closely  related  to  one  another, 

^  A  paper  published  in  "Science,"  1906,  by  the  senior  ?Aithor,  under 
the  title  "The  Actual  Origin  of  Species,"  has  been  freely  quoted  from  in 
this  chapter. 

9  iir 


118 


EVOLUTION   AND  ANIMAL  LIFE 


5  AjCtOAvU-O/^ 


vu/v\jdL<>v. 
"VWOAVVV   Co. 


C)A4>kM.VO\A^    Co 


Pig.  71. — Some  chipmunks  of  California,  showing  distinct  species  produced  through 
isolation.     (From  nature,  by  William  Sackston  Atkinson.) 


GEOGR.'VPHIC   ISOLATION   AND   SPECIES-FORMING      119 

but  not  derived  from  one  anotlier  by  direct  lines  of  descent.  A 
closer  study  indicates  that  some  of  them  '^camc  from  closely 
related  forms  in  remote  geographic  areas,  others  from  antece- 
dent forms  now  extinct,  and  not  more  than  three  or  four  from 
species  still  inha])iting  the  region/' 

Tho  nature  of  any  fauna  bears  an  immediate  relation  to 
the  barriers,  geographic,  climatic,  topograi)hic,  or  bionomic, 
which  may  form  its  boundaries.  By  bionomic  barriers  wo 
mean  any  condition  of  an}^  sort  which  may  check  free  inter- 
bi-eeding,  or  which  may  tend  to  cause  divergence  within  a 
species.  A  thickly  peopled  level  area  may  be  in  this  sense  a 
barrier,  because  it  prevents  the  animals  on  the  one  side  of  the 
area  from  interbreeding  with  those  on  the  opposite  side.  If 
the  two  extremes  have  diverged  to  become  different  species, 
the  individuals  in  the  middle  area,  whose  presence  in  a  sense 
constitutes  the  bionomic  barrier,  are  usually  variously  inter- 
mediate in  the  characters  and  habits  which  they  possess. 

Whenever  the  individuals  of  a  species  move  evenly  over  an 
area,  its  members  freely  interbreeding,  the  character  of  the 
species  remains  substantially  uniform.  Whenever  freedom  of 
movement  and  consequent  freedom  of  interbreeding  is  checked, 
the  character  of  the  species  is  rapidly  altered.  It  is  changed 
even  though  external  conditions  seem  to  be  absolutely  identical 
on  both  sides  of  the  barrier,  and  if  there  is  no  visible  distinction 
in  the  original  stock  on  the  two  sides.  Presumably,  there  are 
subtle  differences  in  the  environment,  producing  changes  in 
the  process  of  selection  and  adaptation.  Doubtless,  there  are 
differences  ec^ually  subtle  produced  by  the  processes  of  varia- 
tion and  their  repetition  by  inheritance. 

The  pregnant  phrase  of  Dr.  Coues  applies  in  these  cases: 
"Migration  holds  species  true:  localization  lets  them  slip." 
In  other  words,  free  interbreeding  swamps  incipient  lines  of 
variation,  and  this  in  almost  every  case.  On  the  other  hand,  a 
barrier  or  check  of  any  sort  brings  a  certain  group  of  individuals 
together.  These  are  subjected  to  a  selection  different  from 
that  which  obtains  with  the  species  at  large,  and  under  these 
conditions  new  forms  are  developed.  This  takes  place  rapidly 
when  the  conditions  of  life  are  greatly  changed,  so  that  a  new 
set  of  demands  is  made  on  the  species,  and  those  individuals  not 
meeting  it  are  at  once  destroyed.  The  ])r()cess  is  a  slow  one, 
for  the  most  part,  when  the  barrier  in  question  interrupts  the 


120  EVOLUTION   AND   ANIMAL   LIFE 

flow  of  life  without  materially  changing  its  conditions.  But 
this  is  practicall}^  a  universal  rule:  A  barrier  which  prevents  the 
intermingling  of  members  of  a  species  will  with  time  alter  the 
relative  characters  of  the  groups  of  individuals  thus  separated. 
These  groups  of  individuals  are  incipient  species,  and  each 
may  become  in  time  an  entirely  distinct  species  if  the  barrier 
is  really  insurmountable.  In  the  great  water  basin  of  the 
Mississippi,  many  families  of  fish  occur  and  very  many  spe- 
cies are  diffused  throughout  almost  the  whole  area,  occurring 
in  all  suitable  waters.  Once  admitted  to  the  water  basin,  each 
one  ranges  widely  and  each  tributary  brook  has  many  species. 
In  the  streams  of  California,  mostl}^  small  and  isolated,  the 
number  of  genera  or  families  is  much  smaller.  Each  species, 
unless  running  to  the  sea,  has  a  narrow  range,  and  closely  re- 
lated species  are  not  found  in  the  same  river.  The  fact  last 
mentioned  has  a  very  broad  application  and  may  be  raised  to 
the  dignity  of  a  general  law  of  distribution. 

Given  any  species  in  any  region,  the  nearest  related  species 
is  not  likely  to  be  found  in  the  same  region  nor  in  a  remote 
region,  but  in  a  neighboring  district  separated  from  the  first 
by  a  barrier  of  some  sort,  or  at  least  by  a  belt  of  country,  the 
breadth  of  which  gives  the  effect  of  a  barrier. 

Always  the  species  nearest  alike  in  structure  are  not 
found  together  nor  yet  far  apart,  and  always  a  check  to 
interbreeding  lies  between.  Where  two  closely  allied  forms 
are  not  found  to  intergrade,  they  are  called  distinct  species. 
If  we  find  actual  intergradation,  the  occurrence  of  specimens 
intermediate  in  structure,  the  term  subspecies  is  commonly 
used  for  each  of  the  recognizable  groups  thus  connected. 

Widely  distributed  across  the  United  States  and  from 
southern  Canada  to  Arizona,  we  have  the  yellow  warbler, 
Dendroica  ccstiva.  This  bird  is  chiefly  yellow,  olive  on  the 
back  with  chestnut  streaks  on  the  sides,  the  tail  feathers  colored 
like  the  bod}^  and  without  the  white  s])ot  on  the  outer  feathers 
shown  in  most  of  the  other  wood  warblers  composing  the  genus 
Dendroica. 

The  yellow  warbler  throughout  its  range  is  very  uniform 
in  size  and  color.  Its  nearest  relative  differs  in  having  a 
shade  less  olive  on  the  back  and  the  brown  streaks  on  the  sides 
narrower.  This  form  is  found  in  the  Sonoran  region,  and,  as 
along  the  Rio  Grande  it  intergrades  with  the  first,  it  is  called 


GEOGRAPHIC  ISOLATION  AXD  SPECIES-FORMIXG      121 

a  subspecies,  Dendroica  (estiva  sonorana.  Further  soutli,  in 
central  Mexico,  tliis  foini  i-uns  larger  in  size  and  is  recorded  as 
Dendroica  a:stiva  dugesi.  Northward,  tlirough  to  Ahiska,  we 
have  an  ally  of  the  parent  bird,  but  smaller  and  still  more 
greenish.     This  is  Dendroica  wstiva  rubif/inosa. 

In  the  West  Indies,  the  golden  warblers  migrate  not  from 
north  to  south,  but  from  the  shore  to  the  mountains^  and, 
possibly  in  consequence  of  the  less  demand  of  flight,  the  wing 
is  shorter  and  more  rounded,  while  the  tail  is  longer.  As  these 
forms  do  not  clearly  intergrade  with  those  of  the  mainland, 
and,  for  the  most  part,  not  with  each  other,  they  are  held  to 
represent  a  number  of  distinct  species,  although  doubtless 
derived  from  the  parent  stock  of  Dendroica  wsiiva.  Some  of 
these  West  Indian  forms  are  relatively  large,  the  wing  more 
than  five  inches  long,  and  the  longest  known  of  these,  the  type 
of  the  species  for  this  reason,  found  in  Jamaica,  is  called  Dendro- 
ica petechia.  On  the  island  of  Grand  Cayman  is  a  similar 
bird,  a  little  smaller,  Dendroica  auricapiUa.  Of  a  deeper 
yellow  than  petechia,  and  equally  large,  is  the  golden  warbler 
of  the  Lesser  Antilles  ranging  from  island  to  island,  from  Porto 
Rico  to  Antigua.  This  form,  first  known  from  St.  Bartholomew, 
is  Dendroica  petechia  hartholemica.  A  smaller  bird,  a  little 
different  in  color,  takes  its  place  in  the  Bahamas.  This  is 
Dendroica  petechia  flaviceps. 

In  Cul^a,  the  golden  warbler  is  darker  and  more  olive,  with 
other  minor  differences  from  the  form  called  hartholemica,  of 
w^hich  it  may  be  the  parent.  This  is  Dendroica  petechia  gund- 
lachi.  A  similar  bird,  but  with  the  crown  distinctly  chestnut, 
is  Dendroica  petechia  aureola,  the  golden  warbler  of  the  Gala- 
pagos and  Cocos  Islands,  off  the  coast  of  Ecuador  and  Peru. 
Scattered  over  other  islands  are  smaller  golden  warblers  with 
the  wing  less  than  fi^-e  inches  long,  and  with  the  crown  tawny 
red,  as  in  anreola.  These  are  known  collectively  as  Dendroica 
riificapilla,  the  type  being  from  Guadeloupe  and  Dominica. 
More  heavily  streaked,  with  the  crown  darker  in  color,  is  the 
?;olde:i  warl)ler  of  Cozumel,  Dendroica  ruficapilla  fiavivertex, 
.jid  with  very  similar  but  with  darker  crown  is  Dendroica 
ruficapilla  flavida,  of  the  island  of  St.  Andrews.  Always,  the 
nearest  form  lies  across  the  barrier,  and  among  these  island 
forms  the  cliief  barrier  is  the  sea.  A^'ith  a  darker  chestnut 
crown    is   Dendroica   ruficapilla   rujopilcata,    of   the   island    of 


122  EVOLUTION   AND   ANIMAL   LIFE 

Curagao,  and  still  darker  bay  is  the  crown  of  Dendroica  ruficapilla 
capitalis,  the  golden  warbler  of  the  Barbadoes. 

Still  other  goldeii  warblers  exist,  with  the  chin  and  throat 
chestnut  as  well  as  the  crown.  One  of  these,  ohve  green  on  the 
back,  is  Dendroica  rufigida,  of  Martinique.  The  others  are 
more  yellow.  One  of  these,  with  the  sides  heavily  streaked, 
inhabits  the  isthmus  region,  Dendroica  erythacoides ,  callad  a 
distinct  species,  because  no  intergradations  have  been  made 
out.  Another,  more  faintly  streaked,  replaces  it  on  the  Atlantic 
coast  from  Yucatan  to  Costa  Rica,  Dendroica  bryanti,  while 
the  Pacific  coast,  f]'om  Sinaloa  to  Costa  Rica,  has  another  form, 
with  still  fainter  markings,  Dendioica  bryanti  castaniceps.  An 
extreme  of  this  iorvn  with  the  tliroat  and  breast  tawny,  but  not 
the  crown,  is  found  in  Jamaica  again  and  is  known  as  Dendioica 
eoa.  In  this  case,  which  is  one  typical  of  most  groups  of  small 
birds,  the  relation  of  the  species  to  the  barriers  of  geography 
is  so  plain  as  to  admit  of  no  doubt  or  question. 

Given  the  facts  of  individual  fluctuation  and  of  heredity, 
it  is  manifest  that  while  nn.tural  selection  may  produce  and 
enforce  adaptation  to  conditions  of  life,  the  traits  which  dis- 
tinguish these  species  bear  little  relation  to  utility.  The 
individuals  which,  separated  from  the  main  flock,  people  an 
island,  give  their  actu<al  traits  to  their  actual  descendants,  and 
-the  traits  enforced  by  natural  selection  differ  from  island  to 
island.  If  external  conditions  were  alike  in  all  the  islands  the 
progress  of  evolution  would  perhaps  run  parallel  in  all  of  them, 
and  the  only  differences  which  would  persist  would  be  derived 
from  differences  in  the  parent  stock.  As  some  difference  in 
environment  exists,  there  is  {i  corresponding  difference  in  the 
species  as  a  result  of  adaptation.  If  great  differences  in  con- 
ditions exist,  the  change  in  the  species  may  be  greater,  mors 
rapidly  accomplished,  and  the  characters  observed  will  bear 
a  closer  relation  to  the  principle  of  utility. 

Doubtless,  wide  fluctuations  or  mutations  in  every  species 
are  more  common  than  we  suppose.  With  free  access  to  the 
mass  of  the  species,  these  are  lost  through  interbreeding. 
Isolate  them,  as  in  a  garden,  or  an  enclosure  or  on  an  island,  and 
these  may  be  continued  and  intensified  to  form  new  species  or 
races.      Any  breeder  or  any  horticulturist  will  illustrate  this. 

It  is  not  claimed  that  species  are  occasionally  associated 
with  physical  barriers,  which  determine  tlioir  range,  and  which 


GEOGRAPHIC    ISOLATION   AND  SPECIES-FORMING      123 

have  been  factors  in  their  formation.  We  claim  tliat  such 
conditions  are  virtually  universal  among  species  as  they  exist 
in  nature.  When  the  geographical  relations  of  the  origin  of  a 
species  cannot  be  shown  it  is  usually  ])ecause  the  species  has  not 
been  critically  studied,  from  absence  of  material  or  from  absence 
of  interest  on  the  part  of  naturalists.  In  a  few  cases,  a  species 
ranges  widely  over  the  earth,  showing  little  change  in  varying 
conditions  and  little  susceptibility  to  the  effects  of  isolation. 
In  other  cases,  there  is  some  possibilit}^  that  saltations,  or 
suddenly  appearing  characters,  may  give  rise  to  a  new  species 
within  the  territory  already  occupied  by  the  parent  form. 
But  these  cases  are  so  rare  that  in  ornithology,  mammalogy, 
herpetology,  conchology,  and  entomology,  they  are  treated  as 
negligible  quantities. 

One  of  the  most  successful  workers  in  this  field  is  Rev.  John 
T.  Gulick,  whose  studies  of  the  locahzation  of  species  and  sub- 
species of  land  snails  in  Oahu  Island  (Hawaii)  have  become 
classical.  According  to  Mr.  Gulick,  the  land  snails  of  the 
wooded  portion  of  Oahu  have  become  split  up  into  about 
175  species  of  land  shells  represented  by  700  or  SCO  varieties. 
He  frequently  finds  a  genus  represented  in  several  successive 
valleys  by  allied  species,  sometimes  feeding  on  the  same  and 
similar  plants.  In  every  case,  the  valleys  that  are  nearest  to 
each  other  furnish  the  most  nearly  allied  forms,  and  a  full  set 
of  the  varieties  of  each  species  presents  a  minute  gradation 
between  the  more  divergent  types  found  in  the  more  widely 
separated  localities.  Similar  conditions  are  recorded  among 
the  land  snails  in  Cuba  and  in  other  regions.  In  fact,  on  a 
smaller  scale,  the  development  of  species  of  land  and  river 
mollusks  has  everywhere  progressed  on  similar  lines  with  that 
of  ])irds  and  fishes.  To  recognize  isolation  as  practically  a 
necessary  condition  in  the  subdivision  of  species  need  not 
necessarily  eliminate  or  belittle  any  other  factor.  Isolation  is 
c.  condition,  not  a  force.  Of  itself  it  can  do  nothing.  Species 
change  or  diverge  with  space  and  with  time:  with  sjmce,  be- 
cause geographical  extension  divides  the  stock  and  l^rings 
new  conditions  to  part  of  it;  with  Ume,  because  time  ])rings 
always  new  events  and  changes  in  all  environment.  The 
beginning  of  each  species  must  rest  wiili  its  variability  of 
individuals. 

One  of  the  most  remarkaljle  cases  of  group  evolution  is 


124  EVOLUTION   AND   ANIMAL   LIFE 

that  of  the  song  birds  of  Hawaii  which  constitute  the  family  of 
Drepanidse.  In  this  family  are  about  forty  species  of  birds, 
all  much  alike  as  to  general  structure,  but  diverging  amazingly 
from  each  other  in  the  form  of  the  bill,  with,  also,  striking 
differences  in  the  color  of  the  plumage.  In  almost  all  other 
families  of  birds  the  form  of  the  bill  is  very  uniform  within 
the  group.  It  is  correlated  with  the  feeding  habits  of  the  bird, 
and  these  in  most  groups  of  wide  range  become  nearly  uniform 
within  the  limits  of  the  family.  With  a  great  range  of  com- 
petition, each  type  of  bird  is  forced  to  adapt  itself  to  the  special 
line  of  life  for  which  it  is  best  fitted.  But  Avith  many  diverging 
possibilities  and  no  competition,  except  among  themselves,  the 
conditions  are  changed,  and  we  find  Drepanidse  in  Hawaii 
fitted  to  almost  every  kind  of  life  for  which  a  song  bird  in  the 
tropics  may  possibly  become  adapted.     (Plate  II.) 

In  spite  of  the  large  differences  to  be  noted  there  can  be 
little  doubt,  as  Dr.  Hans  Gadow,  Mr.  Henry  W.  Henshav>^  and 
others  have  shown,  of  the  common  origin  of  the  Drepanidse. 
A  strong  peculiar  goatlike  odor  exhaled  in  life  by  all  of  them 
affords  one  piece  of  evidence  pointing  in  this  direction.  There 
is,  moreover,  not  much  doubt  that  the  whole  group  is  descended 
from  some  stock  belonging  to  the  family  of  honey  creepers, 
Ccerebidae,  of  the  forests  of  Central  America.  Each  of  the 
Hawaiian  Islands  has  its  species  of  Drepanine  birds,  some  olive 
green  in  color,  some  yellow,  some  black,  some  scarlet,  and  some 
variegated  with  black,  white,  and  golden.  The  females  in 
most  cases,  like  the  young,  are  olive  green.  On  each  island, 
most  of  the  species  are  confined  to  a  small  district,  to  a  single 
kind  of  thicket  or  a  single  species  of  tree,  each  species  being 
especially  fitted  to  these  localized  surroundings.  With  the 
destruction  of  the  forests  some  of  these  species  are  already  rare 
or  extinct.  With  high  specialization  of  the  bill  they  lose  their 
power  of  adaptation.  In  each  of  the  several  recognized  genera 
there  are  numerous  species,  mostly  thus  specialized  and  local- 
ized, relatively  few  species  being  widely  distributed  throughout 
the  islands. 

Most  primitive  of  all,  least  specialized  and  most  like  the 
honey-creeper  ancestry,  is  the  olive  green  Oreoviystis  bairdi  of 
the  most  ancient  island,  Kauai.  This  bird  has  a  small  straight 
bill,  not  unlike  that  of  the  slender-billed  sparrows.  It  is  said 
to  be  the  most  energetic  and  ubicpiitous  of  the  group,  feeding 


Plate  II. — 1,  Chloridops  kona  Wilson,  Hawaii;  2,  Pseudonenior  xanthophrys 
Rothschild:  3,  Hemiqvath^is  procerus  Cabanis,  Kaiuii.     (I'mm  specimens.) 


GEOGRAPHIC   ISOLATION   AND   SPECIES-FORMIXG      125 

on  insects  on  tlie  trunks  of  trees.  If  we  assume  tliiit  Oreo- 
mystis,  or  some  other  of  the  genera  with  sliort  and  slender  ])ills, 
represents  the  original  type  of  Drepanida,  we  have  two  lines  of 
divergence,  both  of  them  in  directions  of  adaptation  to  peculiar 
methods  of  feeding. 

Next  to  Oreomystis.  on  the  one  hand,  we  have  Loxops  and 
Himatione,  with  the  bill  pointed,  a  little  longer  than  in  Oreo- 
mystis, and  slightly  curved  downward.  The  species,  red  or 
golden,  of  these  two  genera  are  distributed  over  the  islands, 
each  on  its  own  mountain  or  in  its  own  particular  forest. 
Vestiaria,  another  genus,  remarkable  for  its  beautiful  scarlet 
plumage,  has  the  bill  very  much  longer  and  strongly  curved 
downward.  Vestiaria  coccinea,  the  iiwi  of  the  islands,  lives 
among  the  crimson  flowers  of  the  ohia  tree  (Metrosideros)  and 
the  giant  lobelia,  w^iere  it  feeds  chiefly  on  honey,  which  is 
said  to  drop  from  its  bill  when  shot.  According  to  Mr.  S.  B. 
Wilson,  the  scarlet  sickle-shaped  flowers  of  a  tall  climbing 
plant  {Strongylodon  lucidus)  found  in  these  forests  ^'  mimic  in 
a  most  perfect  manner  both  in  color  and  in  shape  the  bill  of 
the  iiwi  "  so  that  the  plant  is  called  nukuiiwi  (bill  of  the  iwii). 

The  next  genus,  Drepanis,  has  the  sickle  bill  still  further 
prolonged,  forming  a  segment  of  a  circle,  and  covering  nearly 
fifty  degrees.  Drepanis  pacifica,  one  of  the  species,  has  the  bill 
forming  about  one  fourth  of  the  total  length.  The  species  of 
this  genus,  black  and  golden  in  color,  were  very  limited  in 
range,  and  are  now  nearly  or  quite  extinct.  Still  anotlier 
group  with  sickle  bills,  Hemignathus,  diverges  from  Vestiaria 
in  having  only  the  upper  mandible  very  long  and  decurved, 
the  lower  one  being  straight  and  stiff.  The  numerous  species 
are  mostly  golden  yellow  in  color.  The  group  contains  long- 
billed  forms  like  Hemignathus  procerns  of  Kauai,  and  short- 
billed  forms  like  Heterorhyiichus  olivaceus  of  Hawaii.  In  the 
short-billed  forms  the  two  mandibles  are  c|uite  unlike:  the  upper 
very  slender,  much  curved  and  about  one  foiu'th  the  length  of 
"he  rest  of  the  body,  the  lower  mandil^le  half  as  long  and  thick 
and  stiff.  These  birds  feed  chiefly  on  insects  in  the  dead  limbs 
of  the  koa  trees  in  the  moimtain  forests.  Some  or  all  of  them 
use  the  lower  mandible  for  tai)i)ing  the  trees,  after  the  fashion 
of  woodpeckers,  while  with  the  long  and  flexible  upper  one  they 
reach  into  cavities  for  insects  or  insect  larva;  or  suck  the  honey 
of  flowers. 


126  EVOLUTION   AND   ANIMAL   LIFE 

Mr.  S.  B.  Wilson  remarks:  "Nature  has  shown  great  sym- 
metry in  regard  to  the  species  of  this  genus  {Hemignathus 
inchiding  Heterorhynchus)  to  be  found  in  the  Sandwich  Archi- 
pelago, three  of  the  main  islands  having  each  a  long-billed 
and  a  short-billed  form."  This,  of  course,  is  most  natural. 
Both  long-billed  forms  {Hemignathus)  and  short-l^illed  forms 
{Heterorhynchus)  have  spread  from  the  island  where  they  were 
originally  developed  to  the  other  islands,  each  changing  as  it 
is  isolated  from  the  main  body  of  the  species  and  subjected 
to  natural  selection  under  new  conditions.  With  the  genus 
Heterorhynchus,  the  forms  with  slender  bills  reach  their  culmina- 
tion. 

Going  back  to  the  original  stock,  to  which  Oreomystis 
hairdi  is  perhaps  the  nearest  living  ally,  we  note  first  a  divergeifce 
in  another  direction.  In  Rhodacanthis,  the  bill  is  stout  like 
that  of  the  large  finch,  not  longer  than  the  rest  of  the  head, 
and  curved  downward  a  little  at  the  tip.  The  species  of  this 
genus  feed  largely  on  the  bean  of  the  acacia  and  other  similar 
trees,  varying  this  with  caterpillars  and  other  insects.  The 
stout  bill  serves  to  crush  the  seeds.  In  Chloridops,  the  bill  is 
still  heavier,  very  much  like  that  of  the  grosbeak.  Chloridops 
kona  is,  according  to  Mr.  Robert  Perkins,  a  dull,  sluggish, 
solitary  bird  and  very  silent;  its  whole  existence  ma}^  be  summed 
up  in  the  words  "to  eat."  Its  food  consists  of  the  fruit  of  the 
aaka  (bastard  sandal  tree),  and  as  this  is  very  minute,  its  whole 
time  seems  to  be  taken  up  in  cracking  the  extremely  hard 
shells  of  the  fruit,  for  which  its  extraordinarily  powerful  bill 
and  heavy  head  are  well  adapted. 

"The  incessant  cracking  of  the  fruits,  when  one  of  these  birds  is 
feeding,  the  noise  of  which  can  be  heard  for  a  considerable  distance, 
renders  the  bird  much  easier  to  get  than  it  otherwise  would  be.  Its 
beak  is  always  very  dirty  with  a  brown  substance  adhering  to  it  which 
must  be  derived  from  the  sandal  nuts." 

In  Psittacirostra  and  Pseudonestor  the  bill  suggests  that  of 
a  parrot  rather  than  that  of  a  grosbeak.  The  mandibles  are 
still  very  heavy,  but  the  lower  one,  as  in  Heterorhynchus,  is 
short  and  straight,  while  the  much  longer  upper  one  is  hooked 
over  it.  Pseudonestor  feeds  on  the  larvae  of  wood-boring  beetles 
{Cly tonus)  found  in  the  koa  trees,  {Acacia  jalcata),  while  tlic 


Plate  III. — 1,  Oreomyatis  hairdii  Stejneger,  Kauai;  2,  Hrterorfn/nchus  oliva- 
ceus  La  Fresnaye,  Hawaii;  3,  Drcpanis  funerea  Newton,  Molokai.  (From 
specimens.) 


GEOGRAPHIC   ISOLATION   AND  SPECIES-FORMIXG      127 

closely  related  Psittacirostra  eats  only  fruits,  that  of  the  ieie 
(Freycinetia  arhorea)  and  the  red  miill)erry  (Moms  sapyrifera) 
being  especially  chosen.  In  all  these  genera,  tliere  is  prac- 
tically one  species  to  eacli  ishmd,  except  that  in  some  cases 
the  species  has  not  spread  from  the  mountain  or  ishind  in  wliich 
we  may  suppose  it  to  have  been  originally  developed. 

There  are  a  few  other  song  birds  in  the  Hawaiian  Islands,, 
not  related  to  the  Drepanida).  These  are  derived  from  the 
islands  of  Polynesia  and  have  deviated  from  the  original  types; 
in  a  degree  corresponding  to  their  isolation.  In  the  case  of  the 
Drepanidse,  it  seems  necessary  to  conclude  that  natural  selection 
is  responsible  for  the  physiological  adaptations  characteristic 
of  the  different  genera.  Such  changes  may  be  relatively  rapid, 
and  for  the  same  reason  they  count  for  little  from  the  stand- 
point of  phylogeny.  On  the  other  hand,  the  nonuseful  traits, 
the  petty  traits  of  form  and  coloration  which  distinguish  a 
species  in  Oahu  from  its  homologue  in  Kauai  or  Hawaii,  are 
results  of  isolation.  These  results  may  be  analyzed  as  in  part 
differences  in  selection  with  different  competition,  different 
food  and  different  conditions,  and  in  part  to  hereditary  differ- 
ence due  to  the  personal  eccentricities  in  the  parent  stock  fromi 
which  the  newer  species  was  derived. 

In  these  as  in  all  similar  cases  we  may  confidently  af^m.^ 
the  adaptive  characters  a  species  may  present  are  ilne  to 
natural  selection  or  are  developed  in  connection  with  the 
demands  of  competition.  The  characters  nonadaptive  which 
chiefly  distinguish  species  do  not  result  from  natin-al  selection, 
but  are  connected  with  some  form  of  geographical  isolation 
and  the  segregation  of  individuals  resulting  from  it. 

The  origin  of  races  and  breeds  of  domestic  animals  is  in 
general  of  much  the  same  nature.  In  traveling  over  Eng- 
land one  is  struck  by  the  fact  that  each  county  has  its  own 
breed  of  sheep,  each  of  these  having  its  type  of  excellence  in 
mutton,  wool,  hardiness,  or  fertility,  but  the  breeds  distin- 
guished by  characters  having  no  utility  either  to  sheep  or  ti(>> 
man.  The  breeds  are  formed  primarily  by  isolation.  't\\e-. 
traits  of  the  first  individuals  in  each  region  are  intensifjed  by- 
the  inbreeding  resulting  from  segregation.  Natural  sielectiou 
preserves  the  hardiest,  the  most  docile,  and  the  iwost  fertile: 
artificial  selection  those  which  yield  the  most  wool,  the  iK'st 
mutton  and  the  like.     The  breed  once  cjstablished,  artiticial 


128  EVOLUTION  AND  ANIMAL  LIFE 

selection  also  tends  to  intensify  and  to  preserve  its  nonadaptive 
characteristic  marks.  The  more  pride  the  breeders  take  in 
their  stock,  the  more  certain  is  the  preservation  of  the  breed's 
useless  pecuUarities.  Very  few  of  the  characters  which  usually 
distinguish  a  breed  of  domestic  animals  have  the  shghtest  phys- 
iological value  to  the  species.  Each  of  them  would  disappear 
in  a  few  generations  of  crossing,  and  in  each  race  prized  by  the 
breeder  the  actual  virtues  exist  wholly  independent!}'  of  these 
race  marks. 

Analogous  to  the  race  peculiarities  of  domestic  animals 
are  the  minor  traits  among  the  men  of  different  regions.  Cer- 
tain gradual  changes  in  speech  are  due  to  adaptation,  the  fitness 
of  the  word  for  its  purpose,  analogous  to  natural  selection. 
The  nonadaptive  matters  of  dialect  find  their  origin  in  the 
exigencies  of  isolation,  while  languages  in  general  are  ex- 
plainable by  the  combined  facts  of  migration,  isolation,  and 
the  adaptation  of  words  for  the  direct  uses  of  speech. 

In  the  animal  kingdom  generally  we  may  say  therefore: 
Whenever  a  barrier  is  to  some  extent  traversable,  the  forms 
separated  by  it  are  likely  to  cross  from  one  side  to  the  other, 
thus  23roducing  intergradations,  or  forms  more  or  less  inter- 
mediate betvveen  the  one  and  the  other.  For  every  subspecies, 
where  the  nature  of  the  variation  has  been  carefully  studied, 
there  is  always  a  geographical  basis.  This  basis  is  defined 
by  the  presence  of  some  sort  of  physical  barrier.  It  is  ex- 
tremely rare  to  find  two  subspecies  inhabiting  or  breeding  in 
exactly  the  same  region.  When  such  appears  to  be  the  case, 
there  is  really  some  difference  in  habit  or  in  habitat:  the  one 
form  lives  on  the  hills,  the  other  in  the  valleys;  the  one  feeds 
on  one  plant,  the  other  on  another;  the  one  lives  in  deep  water, 
the  other  along  the  shore.  There  can  be  no  possible  doubt  that 
subspecies  are  nascent  species,  and  that  the  accident  of  inter- 
gradation  in  the  one  case  and  not  in  the  other  implies  no  real 
difference  in  origins. 

For  a  final  example,  we  may  compare  the  species  of  Ameri- 
can orioles  constituting  the  genus  Icterus.  We  may  omit  from 
consideration  the  various  subspecies,  set  off  by  the  mountain 
chains,  and  the  usual  assemblage  of  insular  forms,  one  in 
each  of  the  West  Indies,  and  confine  our  attention  to  the 
leading  species  as  represented  in  the  United  States.  (See 
frontispiece.) 


GEOGRAPHIC   ISOLATION   AND   SPECIES-FORM IXG      129 

The  orchard  oriole,  Icterus  spurius,  has  the  head,  l)ack,  and 
tail  all  black,  the  lower  parts  chestnut,  and  the  body  relatively 
small;  as  shown  by  the  average  measurements  of  different 
parts.  In  the  hooded  oriole.  Icterus  cucullatus,  the  head  is  all 
golden  orange  except  the  throat,  which  is  black,  the  tail  is 
black,  and  the  wings  are  black  and  white.  This  species,  with 
its  subspecies,  ranges  through  southern  California  and  Arizona, 
and  over  much  of  Mexico.  Our  other  orioles  have  the  tail  Vjlack 
and  orange.  In  the  common  Baltimore  oriole,  Icterus  galbida, 
of  the  east,  the  head  is  all  black  and  the  under  parts  orange. 
In  the  equally  common  Bullock  oriole.  Icterus  huUocki,  of  the 
California  region,  the  head  is  yellow  on  each  side,  the  belly 
rather  yellow  than  orange.  The  females  of  all  the  species  are 
plain  olivaceous,  the  color  and  proportions  of  parts  varying 
with  the  different  species,  while  in  the  males  of  each  of  the 
many  species  black,  white,  yellow,  orange,  and  chestnut  are 
variously  and  tastefully  arranged.  Each  species  again  has  a 
song  of  its  own,  and  each  its  own  way  of  weaving  its  hanging 
nest. 

That  which  interests  us  now  is  that  not  one  of  these  varied 
traits  is  clearly  related  to  any  principle  of  utility.  Adaptation 
is  evident  enough,  but  each  species  is  as  well  fitted  for  its  life 
as  any  other,  and  no  transposition  or  change  of  the  distinctive 
specific  characters  or  any  set  of  them  would  in  any  conceivable 
degree  reduce  this  adaptation.  No  one  can  sa}^  that  any  one 
of  the  actual  distinctive  characters  or  any  combination  of 
them  enables  their  possessors  to  survive  in  larger  numbers 
than  would  otherwise  be  the  case.  One  or  two  of  these  traits, 
as  objects  of  sexual  selection  or  as  recognition  marks,  have  a 
hypothetical  value,  but  their  utility  in  these  regards  is  slight 
or  uncertain.  Naturalists  now  look  with  doubt  on  sexual 
selection  as  a  factor  in  the  evolution  of  ornamental  structures, 
and  the  psychological  reality  of  recognition  marks  is  yet  un- 
proved, though  not  impossible.  It  may  be  noted  in  passing, 
that  the  prevalent  dull  yellowish  and  olivaceous  hues  of  the 
female  orioles  of  all  species  seem  to  be  clearly  of  the  nature 
of  protective  coloration. 

It  has  been  shown  statistically  that  certain  specific  charac- 
ters among  insects  have  no  relation  to  the  process  of  selection. 
Among  honey  bees  the  variation  in  venation  of  tlie  wings 
and  in  the  number  and  character  of  the  wing  hooks  is  just  as 


130  EVOLUTION   AND   ANBIAL   LIFE 

'great  among  the  bees  which  first  come  from  their  cells  as  in  a 
series  of  individuals  long  exposed  to  the  struggle  for  existence. 

Among  ladybird  beetles  of  a  certain  species  {Hippodamia 
convergens),  eighty-four  different  easily  describable  "aberra- 
tions" or  variations  in  the  number  and  arrangement  of  the 
black  spots  on  the  wing  covers  have  been  traced.  These 
variations  are  again  just  as  numerous  in  individuals  exposed 
to  the  struggle  for  life  as  in  those  just  escaped  from  the  pupal 
state.  In  these  characters,  there  is,  therefore,  no  rigorous 
choice  due  to  natural  selection.  Such  specific  characters, 
without  individual  utility,  may  be  classed  as  indifferent,  so 
far  as  natural  selection  is  concerned,  and  the  great  mass  of 
specific  characters  actually  used  in  systematic  classification  are 
thus  indifferent. 

And  what  is  true  in  the  case  of  the  orioles  and  the  ladv- 
birds  is  true  as  a  broad  proposition  of  the  related  species  which 
constitute  any  one  of  the  genera  of  animals  or  plants.  All 
that  survive  are  sufficiently  fitted  to  live,  each  individual,  and 
therefore,  each  species,  matched  to  its  surroundings  as  the  dough 
•is  to  the  pan,  or  the  river  to  its  bed,  but  all  adaptation  lying  ap- 
parently within  a  range  of  the  greatest  variety  in  nonessentials. 
Adaptation  is  presumably  the  work  of  natural  selection;  the 
division  of  forms  into  species  is  the  result  of  existence  under 
new  and  diverse  conditions. 


CHAPTER   IX 
VARIATION   AND   MUTATION 

It  becomes  imperative  that  we  should  carry  out  the  most  exact 
research  possible  by  means  of  experiment  and  also  wean  ourselves  of 
the  convenient,  but,  as  it  seems  to  me,  highly  pernicious  habit  of  theo- 
retical explanations  from  general  propositions.  Otherwise  there  is 
great  danger  that  the  bright  ex])ectation  which  Darwin  has  opened  out 
to  us  by  his  theory  may  be  baffled — the  prospect  of  gradually  ])riugiiig 
even  organic  Being  within  reach  of  that  method  of  inquiry  which 
seeks  to  discern  mechanical  efficient  causes. — Semper. 

Thus  far  in  our  discussion  of  evolution  factors  and  theories 
we  have  taken  for  granted  the  actuality  of  the  two  fundamental 
factors,  variation  and  heredity.  No  one  disputes  their  reality; 
nor  does  an3'one  deny  their  fundr.mental  and  indispensable 
character  in  relation  to  the  origin  of  species  and  the  evolution 
of  organisms.  All  the  theories  to  explain  evolution  build  on 
these  two  basic  factors  or  vital  conditions.  The  subjects  of 
doubt  or  denial  are  such  postulated  factors  as  selection,  muta- 
tion, orthogenetic  progress,  etc.;  variation  and  heredity  never. 

But  the  character,  the  influence,  the  regularity  or  irregu- 
larity of  variations,  their  behavior  in  heredity,  whether  trans- 
missible or  not,  whether  acquired  or  congenital,  whether  deter- 
minate or  indeterminate,  etc. — these  are  the  j^roblems  that  the 
factor  variation  or  variability  presents  to  biologists.  Heredity, 
too,  has  its  problems.  These  we  shall  take  u]>  in  another 
chapter. 

That  variations  exist  is  too  ol:)vious  to  everyone  to  need  any 
discussion.  Any  litter  of  kittens  or  jiuppies,  of  mice  or  pigs, 
shows  us  the  differences  in  pattern,  shajie,  and  physiology  of  in- 
dividuals born  at  one  time  and  of  the  same  parents.  In  wild 
nature  the  variations  among  l^rothers  and  sisters  are  no  less  real 
than  among  these  domesticated  animals. 

131 


132 


EVOLUTION  AND  ANIMAL  LIFE 


Collect  a  few  thousand  individuals,  at  one  time  in  one  place, 
of  a  single  species  of  insect,  as  a  spotted  ladybird  beetle;  then 
go  over  these  carefully,  looking  for  variation  in  some  single 
characteristic,  as  the  color  pattern.    What  do  you  find?    Let  us 


F'-G.  72. — Diagram  showing  variation  in  elytral  pattern  of  the  convergent  ladybird, 
Hippodamia  convergens  :   1,  Mode;  2-9,  variations  in  size  of  spots;  10-17,  variations 
by  coalescence  of  spots;  18-40.  variations  by  reduction  in  number  of  spots.     (After 
Kellogg  and  Bell./ 


VARIATIUX   AND  MITATION 


133 


answer  by  calling  attention  lo  Figs.  72,   73,  and  74  and  what 
these   variations    signify.      Note   also    Fig.   75,  showing   the 


Fig.  73. — Diagram  showing  variations  in  elytral  pattern  of  convergent  ladybird. 
Hippodamia  convergens:  1-5,  Variations  by  different  reduction  in  number  of  spots 
in  the  two  elytra;  6-9,  variations  by  conditions  of  spots.     (After  Kellogg  and  Hell.) 


variation  in  elytral  blotching  to  be  found  in  a  series  of  individ- 
uals of  the  California  flower  beetle,  Diabrotica  soror:  see  also 
Fig.  76,  showing  the  vari- 
ations   in     the    black    and 


B 


© 


Q 


yellow  color  pattern  of  the 
abdomen  of  the  common 
yellow  jacket  {Vespa  sp.); 
and  Fig.  77  showing  the 
variation  in  the  pattern  of 
the  prothorax  in  a  series  of 
178  individuals  of  a  common 
Californian  flower  bug,  all 
the£3  individuals  collected 
at  one  time  by  sweeping  a 
net  over  a  few  rods  of  alfalfa 
and  Baccharis  on  the  campus 
of  Stanford  University. 

These  are  all   color   and 
pattern   variations;   but   in- 
sects show  variations  in  structural  parts  as  well.     Fig.  7S  shows 
a  common  red-legged  locust  and  one  of  its  hind  tibiie  enlarged 
10 


FiQ.  74. — Diagram  showing  variation."*  in 
prothoracic  patterii  of  the  convergent 
l;i<i.\"bird,  If ij>i><H/(inii(i  convergens.  (.-Vfter 
Kellogg  ami  Hell.) 


134 


EVOLUTION  AND  ANIMAL  LIFE 


Fig.  75. — Diagram  showing  variations  in  elytral  pattern  of  the  California 
flower  beetle,  Diahrotica  soror.      (After  Kellogg  and  Bell.) 

to  show  the  spines.     In  eighty-nine  individuals  of  this'  species 
of  locust  collected  at  Ithaca,  N.  Y.,  the  number  of  spines  in  the 

outer  row  of  the  right  tibiae 


Ac 


varies  from  nine  to  fifteen, 
in  the  inner  row  from  eleven 
to  sixteen.  One  not  giA^en  to 
the  systematic  study  of  insects 
may  think  spines  on  the  hind 
legs  very  trivial  structures  in- 
deed; but  the  entomologist; 
using  exactly  such  character- 
istics as  the  number  of  these 
structures  as  a  means  in  help- 
ing him  to  distinguish  and 
define  his  species,  knows  how 
considerable  this  variation 
really  is. 

The  dog-days  cicada  (Fig. 

79)  also  has  spines  on  its  hind 

tibiae,  but  only  a  few,  usually, 

indeed,  two.    But  in  any  series 

of  individuals  of  this  insect  some  individuals  will  be  found  with 

but  a  single  spine,  some  with  three,  and  a  few  with  four  even, 

although  the  very  great  majority  will  have  two.     For  example, 


Fig.  76. — Diagram  showing  variation  in 
pattern  in  the  yellow  jacket,  Vespa  ger- 
manica.     (After  Kellogg  and  Bell.) 


VARIATION   AND   MUTATION 


135 


in  a  series  of  98  male  individuals  collected  at  Indianaijoli.s,  In- 
diana, at  one  time,  12  individuals  had  one  spine  in  the  outer  row 
of  the  right  tibitc,  S3  had  two  spines,  2  had  three  spines,  and  one 
had  four  spines.  In  the  outer  row  of  the  left  til)iie  of  the  same 
individuals,  there  were  three  spines  in  6  individuals,  two  in  75, 
and  one  in  17.     In  the  inner  rows  of  tibial  spines  in  these  same 


0°  ^^^} 


Fig.  77. — Diagram  showing  variation  in  pattern  of  the  prothorax  of  a  flower  bug 

(After  Kellogg  and  Bell.) 


individuals  there  were  in  the  riglit  tibia\  five  spines  in  5,  four 
spines  in  40,  three  spines  in  43,  two  spines  in  9,  and  one  spine  in 
1  individual:  in  the  left  tibi?e,  five  spines  in  2  individuals,  four 
spines  in  48,  three  spines  in  39,  and  two  spines  in  8. 

In  the  paper  from  wliich  we  have  taken  these  illustrations 
of  the  actuality  of  variation,  studied  and  statistically  tabulated, 
are  given  the  data  showing  the  actual  extent  and  frecpiency  of 
variations  in  various  characters,  such  as  color  patterns  of  head, 
thorax,  and  abdomen,  character  of  antennal  segments,  ninnber 
of  tibial  spines,  character  of  elytral  striation,  character  of  vcu;,- 


I3u 


EVOLUTION   AND  ANIJMAL   LIFE 


tion,  number  of  wing  hooks,  etc.,  in  two  dozen  different  insect 
species.  Long  ago  Dr.  J.  A.  Allen,  of  the  American  Museum  of 
Natural  History,  gave  similar  data  of  the  actual  variation  in 


'^S^/' 


Fig.    78. — Red-legged    locust,    Melanoplus  Fig.  79. — The  seventeen-year  locust,  Cicada 

femur-rubrum,    and    hind    tibia,    showing  septendecim,  and  its  hind   tibia,  showing 

inner  and  outer  rows  of  spines.     (After  inner  and  outer  spines.      (After  Kellogg 

Kellogg  and  Bell.)  and  Bell.) 

various  familiar  American '  bird  species,  his  data  referring 
chiefly  to  variations  in  dimensions;  as  length  of  whole  body, 
length  of  tail,  of  wing,  of  bill,  of  tarsus  and  claw,  etc. 

CARDINAUS  VIRGINIANUS     58  specimens.  Florida. 


e« 


Tall. 


•  •  •• 


••  ••     • 


••••••••9« 


Length  of  Bird. 

••• 

••••••••     ••• 


Wing. 


••     • 


•  •• 

»•••  • 
•  •••• 
» ••••• 
••••••    I 


Fig.  80. — Diagram  showing  variation  in  length  of  tail,  body,  and  wing  in  fifty-eighL 
specimens  of  the  cardinal,  Cardinalis  (formerly  called  virginianus) ,  from  Florida. 
(After  Allen.) 

And  anyone  with  means  of  collecting  considerable  series  of 
individuals  of  single  species  can,  if  he  but  give  the  time  and 
study  to  it,  reveal  similar  variations  in  almost  any  part  or 
characteristic  of  any  species  or  kind  of  plant  or  animal.     ''  What 


VARIATION  AND  MUTATION 


1  '^' 


parts  vary?"  some  one  asks.     All  parts  vary,  Init  some  more 
than  others. 

Darwin,  in  Chapter  V  of  his  "Origin  of  Species,"  postulated 
certain  so-called  laws  of  variabihty,  which  attempt  to  answer 
this  question,  "What  parts  vary?"     These  so-called    "laws" 

which  to-day  would  hardly 

VARIATION  OF 

ICTERUS  BALTIM0RE.20.^ 


be  dignified  with  the  name 
of  law,  are  summed  up  by 
Darwin  at  the  end  of  this 
chapter  as  follows: 


Tail. 
•  4 


•  • 


wing. 

•  !•••••• 

•;r 

Tarsus. 


•••••  • 


Middle  Toe. 

•  •••  •  • 

•  •••  f • •  • 

/y//?d|  Toe. 

i*. 


"Oiu-  ignorance  of  the  laws 
of  variation  is  profound.  Not 
in  one  case  out  of  a  hundred 
can  we  pretend  to  assign  any 
reason  why  this  or  that  part 
has  varied.  But  whenever  we 
have  the  means  of  instituting 
a  comparison,  the  same  laws 
appear  to  have  acted  in  pro- 
ducing the  lesser  differences 
between  varieties  of  the  same 
species,  and  the  greater  differ- 
ences between  species  of  the 
same  genus.  Changed  condi- 
tions generally  induce  mere 
fluctuating  variability,  but 
sometimes  they  cause  direct 
and  definite  effects;  and  these 
may  become  strongly  marked 
in  the  course  of  time,  though 
we  have  not  sufficient  evidence 
on  this  head.  Habit  in  i)ro- 
ducing  constitutional  peculiarities,  and  use  in  strengthening,  and 
disuse  in  weakening  and  diminishing  organs,  ajipear  in  many  ca.«ii'S 
o  have  been  potent  in  their  effects.  Homologous  j^arts  tend  to 
vary  in  the  same  manner,  and  homologous  parts  tend  to  coIum-c. 
Modifications  in  hard  parts  and  in  external  ])arts  sometimes  affect 
softer  and  internal  parts.  When  one  part  is  largely  develojxMl,  ]>erhaps 
it  tends  to  draw  nourishment  from  the  adjoinin*;  parts:  and  every  ])art 
of  the  structure  which  can  be  saved  without  detriment  will  be  saved. 


Bill,  Length. 
Bill,  Width. 


•  ••••{••        •      • 

Fig.  81. — Diagr.am  showing  variation  in  di- 
mensions in  twenty  male  specimens  of  the 
Baltimore  oriole,  Icterus  galhula  (formerly 
called  haltimore).      (.\fter  .\llen.) 


138  EVOLUTION  AND  ANIMAL  LIFE 

Changes  of  structure  at  an  early  age  may  affect  parts  subsequently 
developed;  and  many  cases  of  correlated  variation,  the  nature  of  which 
we  are  unable  to  understand,  undoubtedly  occur.  Multiple  parts  are 
variable  in  number  and  in  structure,  perhaps  arising  from  such  parts 
not  having  been  closely  specialized  for  any  particular  function,  so  that 
their  modifications  have  not  been  closely  checked  by  natural  selection. 
It  follows,  probably  from  this  same  cause,  that  organic  beings  low  in 
the  scale  are  more  variable  than  those  standing  higher  in  the  scale,  and 
which  have  their  whole  organization  more  specialized.  Rudimentary 
organs,  from  being  useless,  are  not  regulated  by  natural  selection,  and 
hence  are  variable.  Specific  characters — that  is,  the  characters  which 
have  come  to  differ  since  the  several  species  of  the  same  genus  branched 
off  from  a  common  parent — are  more  variable  than  generic  characters, 
or  those  which  have  long  been  inherited,  and  have  not  differed  within 
this  same  period.  In  these  remarks  we  have  referred  to  special  parts 
or  organs  being  still  variable,  because  they  have  recently  varied  and 
thus  come  to  differ ;  but  we  have  also  seen  .  .  .  that  the  same  prin- 
ciple applies  to  the  w^hole  individual;  for  in  a  district  where  many 
species  of  a  genus  are  found — that  is,  where  there  has  been  much  former 
variation  and  differentiation,  or  where  the  manufactory  of  new  spe- 
cific forms  has  been  actively  at  work — in  that  district  and  among 
these  species  w^e  now  find,  on  an  average,  most  varieties.  Secondary 
sexual  characters  are  highly  variable,  and  such  characters  differ  much 
in  the  species  of  the  same  group.  Variability  in  the  same  jDarts  of  the" 
organization  has  generally  been  taken  advantage  of  in  gi^^ng  secondary 
sexual  differences  to  the  two  sexes  of  the  same  species,  and  specific 
differences  to  the  several  species  of  the  same  genus.  Any  part  or  organ 
developed  to  an  extraordinary  size  or  in  an  extraordinary  manner,  in 
comparison  with  the  same  part  or  organ  in  the  alHed  species,  must  have 
gone  through  an  extraordinary  amount  of  modification  since  the  genus 
arose;  and  thus  we  can  understand  why  it  should  often  still  be  variable 
in  a  much  liigher  degree  than  other  jDarts;  for  variation  is  a  long-con- 
tinued and  slow  process,  and  natural  selection  will  in  such  cases  not  as 
yet  have  had  time  to  overcome  the  tendency  to  further  variability  and 
to  reversion  to  a  less  modified  state.  But  when  a  species  with  an  ex- 
traordinarily developed  organ  has  become  the  parent  of  many  modified 
descendants — which  in  our  view"  must  be  a  very  slow  process,  requiring 
a  long  lapse  of  time — in  this  case,  natural  selection  has  succeeded  in 
gi\'ing  a  fixed  character  to  the  organ,  in  however  extraordinary  a 
manner  it  may  have  been  developed.  Species  inheriting  nearly  the 
same  constitution  from  a  common  parent,  and  exposed  to  similar 


VARIATION   AND   MUTATION 


139 


Lacerta  ocellata 


Lacertaviridls 


Neck 
Bodif 

Hind  Legs 
[Tail 


f  • 


Lacerta  agilis 


.Necii 
Bodif 

Hind  Legs 
Tail 


Lacerta  muralis 


Neck 

Body 
Hind  Legs 


Lacerta  velox 


Neck 

.Body 
—.Jlind  Legs 
.....Tail 


Lacerta  deserti 


Neck 

5odg 

HirnJ  Legs 

^amtmmmTbi/l 


1 


Fig.  82. — Diagram  showing  variations  in  dimensions  of  lizards,     (..\fttr  Wallace.) 

influences,  naturally  tend  to  i)resent  analo<:;ou.s  variations,  or  these 
same  species  may  occasionally  revert  to  some  of  the  characters  of  their 
ancient  progenitors.  Althou<2;h  new  and  important  modifications  may 
not  arise  from  reversion  and  analo.s^ous  variation,  such  modifications 
will  add  to  the  beautiful  and  harmonious  diversity  of  nature. 


140 


EVOLUTION   AND  ANIMAL   LIFE 


"Whatever  the  cause  may  be  of  each  slight  difference  between  the 
offspring  and  their  parents — and  a  cause  for  each  must  exist — we  have 
reason  to  beUeve  that  it  is  the  steady  accumulation  of  beneficial  defer- 
ences which  has  given  rise  to  all  the  more  important  modifications  of 
structure  in  relation  to  the  habits  of  each  species." 


Num.  of 
Variftfes. 


Modern  investigation  of  variation,  which  includes  at  least  two 
phases  of  study  that  have  been  developed  since  Darwin's  time, 
namely  the  statistical  and  quantitative,  and  the  experimental 

studv  of  variation,  has  been 
able  to  add  much  information 
about  the  mode  and  the 
character  of  variations,  and 
has  effected  a  sort  of  classifi- 
cation of  them  which  helps  at 
once  to  express  and  to  clarify 
and  organize  our  knowledge 
of  variability.  But  it  has 
added  as  yet  no  great  funda- 
mental generalizations  really 
worthy  to  be  called  laws. 

One  generalization  there  is, 
perhaps,  of  application  and 
value  far  reaching  enough  to 
be  called  law  (although  it  ap- 
plies to  only  a  single  category 
of  variation,  but  a  large  one), 
and  that  is  the  law  formulated 
in  1846  (ten  years  before  Dar- 
win's "Origin  of  Species"), 
by  the  Belgian  anthropologist, 
Quetelet,  on  the  basis  of  the 
examination  of  the  height  and 
chest  measurements  of  soldiers.  As  it  applies  only  to  what 
are  variously  called  fluctuating,  individual,  continuous,  or  Dar- 
winian variations,  we  may  note  before  stating  the  law  the  cur- 
rent mode  of  classifying  the  variations  which  occur  in  plants 
and  animals. 

Variations  may  be  either  congenital  or  acquired:  that  ic, 
may  be  such  as  are  apparently  determined  in  the  organism  £/: 
conception,  or  such  as  are  imposed  on  it  during  its  development 


450 

1, 

\\ 

400 

>\ 

1 

\' 

350 

V 

300 

\\ 

l\ 

\ 

Vl 

', 

250 

■■■ 

/'•" 

\ 

f; 

\  • 

200 

1  ; 

V 

(; 

\ 

150 

\\ 

i 

h 

\ 

100 
50 

y 

\ 

\ 

\ 

■•\ 

r 

n 

> 

•.\ 

N 

*^ 

Cksses-.O  1   234561    89  10 

Fig.  83.  —  Diagram  showing  curves  of 
distribution  of  frequency  of  variation  in 
glands  of  swine.     (After  Davenport.) 


VARIATION   AND   MUTATION  141 

by  the  influence  of  extrinsic  factors.  Or  variations  may  be  di- 
vided into  determinate  and  indeterminate;  that  is,  those  (if  there 
really  are  such)  which  are  apparently  controlled  by  some,  to  us 
unknown,  influences  and  are  by  these  influences  confined  to  cer- 
tain definite  lines  or  directions  of  change;  and,  on  the  other  hand, 
those  which  are*  apparently  wholly  accidental,  or  rather  which 
may  represent  any  conceivably  possible  line  or  kind  of  change. 
Finally,  variations  may  be  distinguished  as  to  their  general 
character  as  discontinuous  and  continuous;  tliat  is,  variations  oc- 
curring irregularly,  mostly  large  and  comparatively  rarely,  and 
small,  abundant  variations  occurring  in  graded  series.  Among 
the  former  are  to  be  ranked  the  occasional  sports  and  monsters 
familiar  to  all  breeders;  while  in  the  latter,  Darwin  believed  him- 
self to  have  at  hand  the  necessary  ever-present  materials  to 
serve  natural  selection  as  a  basis  for  species  transformation. 
Hence  the  shght  but  abundant  and  ever-present  fluctuating 
continuous  variations  are  often  called  "Darwinian  variations." 

Now  the  law  of  Quetelet  ap})lies  solely  to  the  Darwinian 
variations.  The  law  is,  that  these  variations  occur  according 
to  the  law  of  probabilities  (or  law  of  error):  that  is,  that  the 
shghtest  variations  away  from  the  modal  or  average  type  will 
be  the  most  abundant,  and  that  the  number  of  varying  individ- 
uals will  be  progressively  less  the  farther  away  from  the  modal 
type  the  variations  of  these  individuals  are.  That  is,  if  the  vari- 
ations in  some  characteristic  of  a  species  be  determined  for,  say, 
10,000  individuals  of  the  species,  and  tabulated,  and  a  curve 
erected  to  express  graphically  tlie  facts  of  this  variability,  this 
curve  will  practically  coincide  with  that  one  which  would  simi- 
larly express  the  variation,  if  the  variation  actually  occurred 
according  to  the  mathematical  law  of  the  frequency  of  error; 
this  theoretical  curve  being  obtained  by  the  formula  deduced 
originally  by  Gauss  at  the  beginning  of  the  last  century.  Fig. 
83  show^s  graphically  how  certain  studied  cases  of  continuous 
variation  reveal  the  condition  expressed  by  Quetelet 's  law. 

As  compared  with  discontinuous  and  sport  variati(Mi,  con- 
tinuous variation  is  by  great  odds  the  more  common.  Hateson, 
an  English  student  of  variations,  has  attemi)ted  to  show  that 
discontinuous  variations  are  more  conunon  than  is  generally 
believed,  and  has  filled  a  large  volume  with  accounts  and  illus- 
trations of  such  alleged  variations.  Hut  it  has  been  proved 
that  manv  of  these  arc  cases  of  teratogenic  regeneration,  or  ab- 


142  EVOLUTION  AND  ANIIVIAL  LIFE 

normal  restoration  of  injured  parts.  Others,  too,  are  of  a  char- 
acter which,  to  many  people,  will  not  seem  to  be  discontinuous 
at  all,  but  continuous.  For  example,  differences  in  number  of 
antennal  or  tarsal  segments  in  insects  are  called  by  Bateson 
cases  of  discontinuous  variation  if  the  differences  are  only  by 
one  segment.  But  as  the  differences  cannot  well  be  less  than  a 
whole  segment,  variations  in  number  of  segments,  if  represented 
by  all  the  successive  numbers  between  the  lowest  and  highest 
number  of  segments  observed,  may  fairly  be  called  continuous: 
that  is,  strictly  gradatory. 

It  may  be  of  interest  to  note,  for  the  purposes  of  explaining 
by  concrete  examples  the  various  phases  or  categories  of  varia- 
tion already  named,  some  specific  examples  exemplifying  each 
category.  The  following  are  taken  from  a  paper  on  variation  in 
insects,  which  records  a  number  of  statistical  studies  of  varia- 
bility made  by  the  junior  author  of  this  book  and  Mrs.  Bell- 
Smith. 

To  distinguish  absolutely  between  acquired  variation  and 
congenital  (or  blastogenic)  variation  is  a  matter  which  can  be 
done  in  but  comparatively  few  cases.  Whether  a  variation  be 
congenital  or  whether  it  be  acquired  during  the  development  or 
life-time  of  the  individual  showing  it,  this  variation  cannot  be 
recognized  until  after  a  considerable  part  of  the  development 
has  been  undergone;  if  it  is  a  variation  in  an  adult  structure  or 
function,  all  of  the  development  must  have  been  completed. 
The  variation  is  apparent  only  after  it  is  unfolded:  only  after 
the  part  it  appears  in  has  reached  its  definite  stage  of  completed 
growth  and  development. 

Nov\^,  who  is  to  say  whether  this  variation  was  or  was  not 
imposed  on  the  individual  showing  it,  during  this  long  develop- 
ment and  immature  life  as  a  result  of  some  external  influence 
brought  to  bear  on  the  varying  part  during  the  development? 
We  know  that  such  extrinsic  influences  do  modify  parts  and 
functions  during  individual  development,  and  so  we  must  be 
very  careful  when  we  claim  that  this  or  that  variation  is  con- 
genital and  not  acquired.  Yet,  how  all-important  it  is  to  make 
the  distinction  is  apparent  when  we  recall  the  fact  that  most 
biologists  are  agreed  that  acquired  characters  (variations)  can- 
not be  inherited,  so  that  new  species  can  be  built  up  only  on 
the  basis  of  congenital  characteristics. 

In  the  c^se  of  insect  variations,  a  criterion  for  distinguishing 


VARIATION  AND  MUTATION  143 

between  the  congenital  and  acquired  condition  is  at  hand, 
thanks  to  the  unusual  character  of  the  development  of  certain 
specialized  insects,  namely,  all  those  that  undergo  a  complex 
metamorphosis. 

"  Without  by  any  means  exhausting  the  subject  of  the  postcmbry- 
onic  development  of  insects,  entomologists  have  become  sufficiently 
well  acquainted  with  the  phenomena  attending  this  development  to  be 
able  to  confirm  absolutely  (in  essential  characters)  Weismann's  dis- 
coveries in  the  larva  of  the  '  imaginal  discs '  as  the  independent  embry- 
onic centers  from  which  develop  the  ^vings,  legs,  antennae,  and  some 
other  parts  of  the  winged  adults  (imagines)  of  insects  with  comjjlete 
metamorphosis.  That  is  to  say,  in  all  the  insects  which  hatch  from  the 
egg  in  a  larval  condition  markedly  different  from  the  definitive  condi- 
tion of  the  species  in  its  fully  developed,  mature  stage,  many  of  the 
adult  organs,  as  the  external  parts  of  the  head,  and  the  legs  and  wings, 
are  produced  not  by  a  gi'adual  development,  growth,  and  transforma- 
tion of  the  corresponding  larval  parts,  but  by  a  special  development  in 
late  larval  life  and  during  the  pupal  stage,  the  final  structures  being 
formed  from  small  groups  of  previously  undifferentiated  subembryonic 
cells.  These  cells  are  derived,  in  the  case  of  the  external  })arts  just 
named  chiefly  from  invaginations  of  the  larval  cellular  skin  layer.  In 
the  larva  (maggot)  of  a  house  fly,  for  example,  there  are  no  functional 
legs  or  wings:  there  are  no  external  signs  (buds,  pads)  of  these  organs  at 
any  time  in  the  larval  stage. 

"In  the  larval  hfe  there  can  be  no  possible  molding  influence  on 
these  future  adult  organs  of  the  nature  of  a  direct  resi)onse  or  reaction 
to  the  immediate  environment.  We  might  assume  such  an  influence 
possible  if  the  \\ings  and  legs  were  slowly  transforming  external  struc- 
tures subject  to  attempts  at  or  actual  functional  use  in  flight  or  crawling 
during  the  larval  life.  At  pupation,  the  win«is  and  legs  suddenly 
appear  as  external  parts,  but  still  equally  functionless,  and  now  wholly 
concealed  and  protected  by  the  opaque  chitinized  wall  of  the  pupariurn. 
With  the  final  issue  of  the  adult,  the  wings  and  legs  ai)i)ear  for  the  first 
time  in  functional  condition,  and  with  the  simple  need  of  unfohliui:. 
expanding,  and  drying  the  outer  wall,  an  operation  re(iuiring  but  feu- 
moments,  they  appear  at  this  time  in  their  definitive  fully  developed 
condition.  The  wings  have  the  arrangement  of  veins  and  number  of 
spines  and  fringing  hairs;  the  legs  have  the  armature  of  spines  and 
spurs  and  the  number  of  segments  whieh  they  retain  unchanged  throuixh 
the  short  or  longer  adult  life.     The  wings  and  legs  of  the  adult  of  all 


144  EVOLUTION  AND  ANIMAL  LIFE 

insects  with  complete  metamorpliosis — and  the  insects  of  this  category 
include  all  the  beetles  (Coleoptera),  two-winged  flies  (Diptera),  moths 
and  butterflies  (Lepidoptera),  ants,  bees,  wasps,  gall  flies  and  ich- 
neumons (Hymenoptera),  and  some  other  orders — are  exposed  during 
their  development  to  just  one  type  of  extrinsic  influences,  namely 
those  of  nutrition,  temperature,  humidity,  etc.  These  influenceG 
affect  the  whole  body  and  metaboHsm  of  the  body-developing  insect. 
But  they  have  no  direct  relation  to  specific  parts. 

"An  important  special  environing  condition  of  life,  and  one  that 
certainly  works  direct  and  obvious  influence  on  the  body  wall  of  certain 
animals,  is  what  may  be  called  the  chromatic  condition  of  the  environ- 
ment. Color  and  pattern  adapted  to  the  needs  of  protection  or  ag- 
gression are  phenomena  familiar  throughout  the  animal  series.  Most 
of  such  color  and  pattern  conditions,  catalogued  under  the  head  of 
protective  resemblance,  mimicry,  warning  colors,  etc.,  are  fixed  con- 
ditions as  far  as  the  individual  is  concerned,  presumably  brought 
about  by  the  age-long  action  of  natural  selection. 

''Not  a  few  animals  display  the  capabihties  of  achieving  marked 
adaptive  changes,  i.  e.,  acciuired  variations,  during  their  immature  life 
(postembryonic  development).  But  it  is  obvious  that  insects  of  com- 
plete metamorphosis,  which  possess  in  adult  stage  a  color  scheme  and 
pattern  wholly  different  from  that  of  the  larva  or  pupa  and  one  which 
is  not  apparent  until  it  appears  in  fixed  definitive  condition  on  the 
emergence  (and  drying)  of  the  imago  from  the  pupal  cuticle,  cannot  be 
conceived  to  show,  in  their  color  pattern,  variations  due  to  individual 
adaptive  changes.  That  is,  variations  in  this  color  pattern  among  the 
individuals  of  a  species  are  not  acquired,  but  are  strictly  congenital, 
except  in  so  far  as  they  are  produced  by  the  general  influences  of 
nutrition,  temperature,  etc.,  working  without  reference  to  the  external 
chromatic  conditions  of  the  environment. 

''Even  such  all-pervading  influences  as  nutrition,  temperature, 
humidity,  and  light  maj^  be,  and  in  many  cases  obviously  are,  so  nearly 
practically  identical  for  all  the  members  of  one  brood,  or  even  for  all 
the  individuals  of  the  species,  that  they  can  have  little  or  no  influence 
in  causing  variations.  For  conspicuous  example,  the  case  of  the  honey 
bee  may  be  noted.  Here,  all  the  larvae  live  side  by  side  under  identical 
conditions  (those  of  the  hive)  of  temperature,  humidity,  and  light,  and 
the  distribution  of  exactly  similar  food  to  them  in  similar  quantity  is 
probably  as  nearly  exactly  uniform  as  could  be  guaranteed  under  our 
most  careful  artificial  experimental  conditions.  The  pupae  are,  more- 
over, under  identical  conditions  of  temperature,  moisture,  and  light,  so 


VARIATION    AND   MUTATION  145 

that  when  the  adults  issue,  the  variations  to  be  found  in  any  of  their 
parts  may  with  complete  confidence  be  ascribed  to  prenatal  influences, 
to  intrinsic  causes.  They  are  purely  blastogenic.  Similarly,  the  con- 
ditions of  hfe  of  the  developing  individuals  of  all  the  other  social 
insects,  the  termites,  ants,  and  social  wasps,  are  practically  identical. 

"The  variations,  therefore,  in  the  color  pattern  of  Diabrotica  (Fig. 
75),  Hippodamia  (Figs.  72,  73  and  74),  and  Vespa  (Fig.  76)  (insects 
of  complete  metamorphosis  with  all  adult  external  structures  never 
exposed  to  outside  conditions  until  in  definite  unchangeable  condition), 
are  congenital  variations.  Of  the  same  nature  are  also  the  structural 
variations  in  the  character  of  the  venation  and  the  number  of  wing 
hooks  in  the  honey  bee  (see  Fig.  94).  But  the  variations  in  the  pat- 
tern of  the  prothorax  of  the  flower  bug  (Fig.  77),  and  in  the  number 
of  spines  on  the  tibiae  of  the  red-legged  locust  (Fig.  78),  and  the  cicada 
(Fig.  79),  may  be  in  part  acquired.  In  these  latter  cases  the  insects, 
not  having  a  complete  metamorphosis,  have  during  their  immature 
life  these  color  and  structural  characters  in  formative  condition,  and 
to  some  extent  in  use.  They  are  therefore  exposed  to  the  continuous 
influence  of  their  environment." 

It  might  be  thought  that  we  could  determine  \vhether  varia- 
tions are  congenital  or  acquired  in  cases  in  which  we  are  thor- 
oughly acquainted  with  the  character  of  the  environment  or  ex- 
trinsic influences  which  have  surrounded  the  individuals  during 
their  development.  In  experimental  cases  w^e  can  control  this 
environment  and  make  it  identical  for  all  of  a  given  lot  of 
individuals,  or  measurably  varying  for  different  lots.  Then 
by  comparison  we  can  determine  what  characteristics  still  vary 
among  those  individuals  exposed  to  identical  environment  — 
these  variations  should  be  congenital — and  what  new  kinds  of 
variations  appear  in  those  individuals  exposed  to  different  en- 
vironments— these  should  be  acquired  variations.  This  has 
been  done  experimentally  for  silkworm  moths.  By  varying 
the  food  supply,  etc.,  marked  variations  have  been  produced  in 
tlis  size  of  larvae  and  moths,  weight  of  silken  cocoons,  duration 
of  larval  stages  (instars).  These  variations  are  manifestly 
accpiired,  and  wherever  in  nature  simj^le  variations  in  dimen- 
sions are  found  among  individuals  of  a  species,  this  is  due  un- 
doubtedly, to  greater  or  lesser  extent,  to  differing  conditions  of 
nutrition.  But  we  know  well  that  a  practically  identical  food 
supply  given  to  domesticated  animals  or  human  beings  can 


146 


EVOLUTION  AND  ANIMAL  LIFE 


never  make  all  the  individuals  of  a  single  brood  or  family  of  tlie 
same  size.  Part  of  the  dimensional  variation  is  due,  therefore, 
to  congenital  causes.  In  a  beehive,  the  condition  of  temper- 
ature, humidity,  and  food  supply  are  practically  identical  for 
all  the  developing  bees,  and  yet  bees  born  of  eggs  laid  by  a 

single  queen,  reared  at  the  same  time  in 
the  same  hive,  var}^  largely  in  such  easily 
determinable  and  important  matters  as 
venation  of  the  wings,  number  of  hooks 
used  in  holding  the  two  wings  of  one  side 
together,  color  pattern,  etc.  Undoubtedly, 
these  variations  are  strictly  congenital,  hence 
inheritable,  and  therefore  of  a  character  to 
serve  as  a  basis  for  species  change. 

With  regard  to  examples  of  continuous 
and  discontinuous  variations,  we  take  the 
following  from  the  paper  on  "Variation  in 
Insects'': 


Fig.  84.  —  Head  with 
one  prong  of  horns 
markedly  different 
from  the  other. 
(After  Bateson.) 


"By  continuous  variations  we  refer  to  those 
variations  mentioned  above,  variously  called 
fluctuating,  individual,  etc.,  which  are  present  in  any  series  of  indi- 
viduals of  a  species,  and  which  cluster  about  the  modal  or  most 
abundantly  represented  forms  of  the  species,  as  would  be  expected 
from  the  law  of  error  (law  of  probabilities)  dis- 
cussed above. 

"Morgan,  in  'Evolution  and  Adaptation,'  ob- 
jects to  the  use  of  '  continuous '  as  a  descriptive 
name  for  these  variations,  on  the  ground  that  the 
word  suggests  persistence  or  continuity  through 
successive  generations.  It  seems  to  us,  however, 
that  the  name  is  an  apt  one,  if  '  continuous '  be 
taken  to  mean  that  the  occurring  variations  in 
any  (sufficiently  large)  set  of  individuals  form  a 
continuous  series,  the  extremes  being  connected 
or  immediately  merging  into  each  other  by  a 
series  of  small  gradatory  steps.  By  'discontinuous'  variation,  we 
would  mean,  in  contrast  to  continuous,  such  considerable  and  radical 
changes  as  have  been  variously  called  single  variations,  sports,  saltations, 
mutations,  etc. ;  that  is,  variations  which  are  not  members  of  graded 
series  and  do  not  group  themselves  in  orderly  manner  about  the  mod^l 


Fig.  85.— Turtle  with 
two  heads.  (After 
Bateson.) 


VARIATION  AND  MUTATION 


14: 


Fig.  86.— Child  with  six 
toes  on  each  foot.  (After 
Bateson.) 


Species  form  according  to  the  law  of  error.  Although  often  not  large, 
they  are  yet  rarely  so  minute  as  those  differences  which  distinguish  the 
adjacent  members  in  any  series  of  individuals  arranged  on  a  basis  of 
continuous  or  fluctuating  variation.  Mutations,  according  to  the  usage 
of  de  Vries,  discontinuous  variations  may  or  may  not  be.  Thus,  all 
mutations  might  be  called  discontinuous 
variations,  although  not  all  discontinuous 
variations  are  necessarily  de  Vriesian  muta- 
tions, that  is,  certain  to  breed  true  under 
varying  conditions  of  environment. 

"Asa  matter  of  fact,  not  all  continuous 
variation  follows  the  law  of  error :  the  curve 
or  polygon  of  frequency  is  not  infrequently 
an  unsymmetrical  one:  'skewness' prevails; 
that  is,  the  highest  part  of  the  curve  may  be 

nearer  one  end,  or  the  curve  may  even  be  bimodal.  But  neverthe- 
less the  'continuity'  of  the  variations  is  unmistakable.  In  a  suffi- 
ciently large  series  the  extremes  of  the  range  are  perfectly  connected 
with  the  mode  or  modes  and  hence  with  each  other  by  gradatory  steps 
very  small  in  size.  Whatever  the  largeness  of  the  difference  between 
the  extremes,  any  two  adjacent  members  of  the  series  are  hardly  distin- 
guishable. This  gradual 
kind  of  variation,  in- 
sensible, but  yet  effective 
(as  regards  widely  se])a- 
rated  members  of  the 
series),  is  most  typically 
illustrated  in  cases  of 
what  Bateson  calls  'sub- 
stantive' variation,  that 
is,  where  the  varying 
characteristic  is  one  of 
pattern,  of  length,  width, 
or  bulk,  of  the  curving 
of  a  vein  or  leg  or  sj)ine. 
Excellent  examj)les  of  this 
continuous  substantive  variation  are  presented  by  the  abdominal  and 
face  patterns  of  Vesjm  (see  Fig.  76),  and  the  clytral  i)attern  of  Din- 
brotica  (see  Fig.  75). 

"According  to  Bateson,   variations   in   number  of  antennal   and 
tarsal  segments,  number  of  spines,  hairs,  or  other  processes,  and  other 


Fig.  87. — Eyestalks  of  a  decapod  dissected  out: 
on  the  right  an  antenna  has  regenerated  out  in 
place  of  an  amputated  eye;  opt.,  optic  nerve. 
(After  Herbst.) 


148 


EVOLUTION  AND  ANIMAL  LIFE 


such  numerical  or,  as  called  by  him,  meristic  variations,  must  be  looked 
on  as  different  in  kind  from  the  substantive  variations — those  capable 
of  perfect  merging  from  one  condition  to  another — in  other  words, 
practically  incapable  of  quantitative  measurements.  These  meristic 
variations  are  called  discontinuous  by  Bateson.  Typical  examples  are 
the  variation  in  the  number  of  the  costal  wing  hooks  in  bees  and  ants, 
the  number  of  tibial  spines  in  the  locust  and  cicada,  the  number  of 
metathoracic  tactile  hairs  in  biting  bird  lice,  etc.  But  when  one  stops 
to  consider  the  fact  that  in  all  these  cases  variation  could  hardly  occur 


•s.j.>tet|^^f  y^^.rf'-   •-- 


£f 


Fig.  88. — Variations  in  pattern  of  wings  of  Peronea  cristana.     (After  Clark.) 


by  any  steps  less  than  those  of  one  hook  or  one  spine  or  one  hair,  that 
a  half  hook  or  half  antennal  segment  is  inconceivable,  serious  doubts  as 
to  the  validity  of  Bateson's  classification  of  variations  as  continuous 
and  discontinuous  will  certainly  result.  The  doubt  is  strengthened 
by  the  difficulty  of  a  clean  classification  presented  by  such  cases  as  that 
of  Hippodaviia  convergens  (Figs.  72,  73  and  74).  Here  we  have  a 
substantive  variation  in  pattern,  appearing,  however,  in  such  a  way  as 
to  demand  numerical,  i.  e.,  meristic,  expression.  One  specimen  has 
nine  elytral  spots,  another  ten,  another  eleven,  and  so  on;  the  whole 
range  is  indeed  from  naught  to  eighteen,  with  every  number  between 
represented,  each  by  various  combinations  of  spots. 

"  But  it  is  conceivable,  and  indeed  is  really  the  case  among  our 
specimens,  that  these  spots  might  be  either  of  normal  size,  or  of  any 
lesser  size  down  to  the  limits  of  \dsibiUty.  Some  of  the  spots  are  of 
the  diameter  of  pin  points,  some  of  the  pin  shaft,  and  some  of  pin 
heads.     There  is  perfect  gradation  and  continuity  in  this  variation. 


VARIATION  AND  MUTATION 


140 


And  even  in  such  cases  as  variations  in  spines  and  hairs,  this  gradation 
might  exist:  and  indeed  it  docs.  Although  in  our  consideration  of  the 
variation  in  the  number  of  the  tibial  spines  of  the  locust  and  cicada 
and  in  the  number  of  the  tactile  hairs  of  the  bird  lice,  we  have  referred 
to  these  variations  only  numerically,  i.e.,  meristically,  as  a  matter  of 
fact  there  are  obvious  differences  in  the  length,  i.  e.,  size,  of  the  spines 
and  hairs,  so  that  it  would  be  wholly  fair  to  break  down  the  unit  differ- 
ences and  speak  of  differences  by  one  quarter,  one  third,  and  two  thirds 
of  a  spine.  For  the  tibial  spines  of  the  locust,  we  have  actually  re- 
corded the  conditions  in  the  form  of  frac- 
tions. But  in  the  case  of  a  hook  or  an 
antennal  or  a  tarsal  segment  it  is  a  miit  or 
nothing. 

''To  our  mind,  the  distinction  between 
substantive  and  meristic  variation  is  not 
at  all  equivalent  to  a  distinction  between 
continuous  and  discontinuous  variation. 
It  is  a  distinction  between  two  categories 
of  variation  only  in  that  one  category  in- 
cludes such  conditions  as  permit  more 
readily  of  extremely  slight,  nearly  insensi- 
ble, practically  unmeasurable  differences, 
as  those  of  pattern  or  shape  or  extent, 
while  the  other  category  includes  partic- 
ularly conditions  in  which  any  variation 
must  of  necessity  be  fairly  obvious,  and 
usually  capable  of  numerical  expression. 

"But  we  believe,  nevertheless,  that  variations  really  discontinuous 
occur  among  insects.  For  example,  the  occurrence  of  interpolated, 
wholly  new,  and  complete  cells  (determined  by  the  presence  of  new 
cross  veins  or  branches  of  longitudinal  veins)  in  the  fore  and  hind 
■wangs  of  drone  honey  bees  (Figs.  93  to  96)  and  the  occurrence  of 
curious  malformations  of  venation  among  drone  bees  must  be  looked 
on  as  sports  or  truly  discontinuous  variations.  The  regular  occurrence 
of  a  four-segmented  foot,  jjerfectly  complete,  functional  in  those  lunner- 
ous  specimens  of  cockroach  (Fig.  89),  in  which  natural  regeneration 
has  taken  place,  may  be  looked  on  as  an  example  of  discontinuous 
variation.  Although  no  difference  in  tarsal  segments  less  than  that  of 
one  is  conceivable,  it  is  quite  conceivable  that  the  foot  with  one  fewer 
than  the  normal  number  might  be  in  such  condition  that  it  would  l^e 
obviously  a  five-segmented  foot  vrith  one  segment  dropped  out :  in 
11 


Fig.  89. — Cockroach,  showing 
varying  number  of  tarsal  seg- 
ments in  legs.  (After  Kellogg 
and  Bell.) 


150  EVOLUTION  AND  ANIM.\L  LIFE 

other  words,  that  when  compared  with  a  normal  five-segmented  foot  it 
would  appear  to  be  a  modification  of  such  a  foot  with  some  one  segment 
wanting.  But  that  condition  is  not  at  all  what  appears  after  the  cock- 
roach regenerates  a  foot.  The  new  foot  is  only  very  little,  if  any, 
shorter  than  the  normal  five-segmented  foot  (see  Fig.  89) :'  one  cannot 
say  that  it  is  precisely  this  or  that  segment  which  is  lost.  It  is  a  new 
kind  of  foot,  apparently  just  as  capable,  as  'fit,'  as  useful  as  the  five- 
segmented  kind.  We  have  regularly  occurring,  in  these  cases  of  re- 
generation, the  development  of  an  entirely  changed  organ,  similar  as 
a  whole  to  the  old  one,  but  different  from  it  in  all  its  parts;  this  differ- 
ence not  being  one  of  incompleteness,  or  serial  addition  or  subtraction, 
but  the  difference  of  newness.     It  is  the  regenerative  mutation  of  an 


organ 


!" 


In  five  years  of  experimental  rearing  of  the  silkw^orms  for 
the  sake  of  studying  phenomena  of  heredity  and  variation,  the 
junior  author  has  been  able  to  record  numerous  cases  of  discon- 
tinuous or  sport  variation  such  as  the  absence  of  the  usually 
well-developed  caudal  horn  of  the  larva,  melanism  in  larvae, 
double  cocooning  or  absence  of  cocoon  in  the  pupal  condition, 
congenital  monstrous  loss  of  a  w^hole  wing  in  the  adult,  striking 
aberration  of  the  wing  pattern  in  the  adult,  etc.  But  the  great 
mass  of  variation  ever  present  and  readily  observable  among 
the  scores  of  thousands  of  silkworm  individuals  reared  and 
carefully  scrutinized  has  been  of  the  continuous  (fluctuating  or 
Darwinian)  type. 

A  special  type  or  kind  of  discontinuous  variation,  that 
exemplified  by  the  so-called  de  A^riesian  mutations,  is  discussed 
at  the  end  of  this  chapter. 

The  matter  of  determinate  A^ariation  is  discussed  as  follows 
in  the  same  paper: 

"The  theory  of  determinate  variation  is  based  on  the  hypothesis 
that  fluctuating  variations  are  not  in  all  cases,  nor  necessarily  in  any 
case,  purely  fortuitous  and  scattering,  but  that  because  of  some  in- 
trinsic or  extrinsic  influence  they  tend  to  occur  along  definite  or 
determinate  lines.  The  need  for  the  theory  rests  on  the  claimed  inad- 
equacy of  slight  fortuitous  variation  in  offering  selection  a  sufficient 
'handle'  for  action.  The  greatest  logical  difficulty  with  the  theory  is 
that  none  of  the  influences  which  are  known  is  adequate  to  cause  such 
an  effect  as  that  of  producing  persistent  determinate  variations.  In 
the  case  of  any  developing  individual,  determinate  variation  can  be 


VARIATIOX   AND   Ml'TATION  151 

attained  by  controlling^  the  environment  (kind  and  quantity  of  foorl, 
degree  of  temperature,  humidity,  and  light,  etc.),  but  if  such  variations 
(modifications)  acquired  during  development  are  not  inherited,  there 
will  be  no  advance,  generation  after  generation,  along  any  line.  There 
will  be  no  cumulative  effect  of  such  determinate  variation.  The  con- 
stant re})etition  of  a  certain  environment  on  generation  after  genera- 
tion of  a  certain  species  would  of  course  produce  a  constant  repetition 
of  certain  individual  modifications  (orthoplasy),  but  we  do  not  know  as 
yet  of  any  actual  effect  on  the  species  of  such  persistent  ontogcnic 
variations. 

"The  need,  however,  for  some  such  factor  in  species-forming  as  de- 
terminate variation  is  obvious  and  strongly  felt.  There  are  certainly 
few  selectionists  left  who  honestly  believe  that  the  minute  fluctuating 
variations  in  pattern,  in  size,  in  curve  of  a  vein,  in  length  of  a  hair,  etc., 
have  that  life-and-death  value  which  is  the  sole  sort  of  value  that  an 
'advantageous  variation'  must  have  to  be  a  serviceable  handle  for  the 
action  of  natural  selection.  As  a  matter  of  fact,  no  systematist  will 
have  escaped  having  had  it  distinctly  impressed  on  him  that  he  recog- 
nizes differences  in  the  pattern  of  ladybird  beetles,  in  the  number  of 
fin  rays  in  fishes,  in  the  branching  of  a  vein  in  flies'  wings,  that  no 
enemy,  no  agent  of  natural  selection,  can  recognize,  at  least  to  the 
extent  of  pronounciuj^-  sentence  of  death  (or  not  pronouncing  jt)  on 
its  basis.  And  further,  no  biologist  really  satisfies  himself  with  the 
worn  statement :  '  We  must  not  presume  to  judge  the  value  of  these  triv- 
ial, these  microscopic  differences,  for  we  do  not  know  all  the  comj^lex 
interrelation  and  interaction  of  the  organism  and  its  environment.' 
We  do  not;  but  we  do  know  for  many  cases  that  such  differences  are 
not  actually  of  Hfe-and-death  selective  value,  and  reason  compels  us  to 
believe  to  a  moral  certainty  that  in  other  cases  these  fortuitous  trivi- 
alities have  similar  lack  of  life-and-death  importance. 

''Directly  touching  this  point  are  our  data  of  the  variation  of  series 
of  honey  bees  collected  from  free-flying  individuals  after  exposure 
as  adults  to  the' rigors  of  outdoor  life,  as  compared  with  the  variation 
in  the  series  of  bees,  adults,  but  collected  just  when  issuing  from  the 
cells  before  being  exposed  as  adults  in  any  way  to  the  external  dangers 
of  hving.  Series  of  both  drones  and  workers  representing  both  exposed 
and  unexposed  individuals  were  studied.  The  results  of  this  examina- 
tion are,  that  the  variation  among  the  exposed  individuals  is  no  less 
than  that  among  the  unexposed  individuals.  Tiiis  means  that  these 
various,  mostly  slight,  blastogenic,  variations  (although  in  such  im- 
portant organs  as  the  wings);  which  occur  among  bees  at  the  time  of 


152 


EVOLUTION  AND  ANBL^L   LIFE 


360 


rrr 


320 


280 


240 


200 
160 
120 


40 


Classes  [  ^ 
Vanates3g3'55 


64 


their  issuance  as  active,  winged  creatures,  are  not  of  sufRcient^dvan- 
tage  or  disadvantage  to  the  individuals  to  lead  to  a  weeding  out  by- 
death  or  sa\ang  of  such  varying  indi\iduals  by  immediate  selective 
action.  "Wliatever  the  rigor  and  danger  of  the  outdoor  bee  life,  these 
variations  seem  to  be  insufncient  to  cut  any  figure  in  the  persistence  or 
nonpersistence  of  any  lndi^^dual  in  the  face  of  this  rigor. 

"A  case  which  really 
seems  to  illustrate  deter- 
minate variation  is  that  of 
the  variation  of  the  flower 
beetle,  Diabrotica  so7'or  (Fig. 
75).  Among  a  thousand  in- 
dividuals collected  on  the 
University  campus  in  1895,  a 
certain  condition  of  variation 
in  the  elytral  pattern  exists, 
as  represented  gi-aphically  by 
Fig.  90.  In  1901  and  1902, 
other  thousands  collected 
from  the  same  place  and 
examined  to  determine  the 
condition  of  the  variation  in 
this  pattern,  show  a  dis- 
tinctly different  status,  as  il- 
lustrated in  Figs.  91  and  92. 
(To  be  sure  that  a  series  of 
a  thousand  individuals  really 
reveals  the  conditions  of  this 
pattern  variation,  repeated 
series  of  1,000  individuals 
each  were  examined  and 
found  jDractically  identical.) 
The  difference  in  the  varia- 
tion status  between  the  1895  lot  and  the  1901-2  lots  consists  in  the 
dominance  in  1901-2  of  one  of  the  two  modal  conditions  found  to 
exist  in  the  species,  which  in  1895  was  not  the  dominant  one.  There 
has  been  a  marked  change  in  seven  years,  not  in  the  pattern  itself 
but  in  the  prevalence  or  dominance  of  one  type  of  pattern.  Has  the 
change  been  brought  about  by  natural  selection?  Or  is  it  the  result 
of  a  determinate  variation  caused  by  we  know  not  what  intrinsic  or 
extrinsic  factors  ? 


MISCEL 


203  '200  total  905 


Pig.  90. — Frequency  polygon  of  variation  of 
elytral  pattern  in  905  specimens  of  the  Cali- 
fornia flower  beetle,  Diabrotica  soror,  collected 
at  Stanford  University,  1895.  (After  Kellogg 
and  Bell.) 


Variation  and  mutation 


153 


360 


3Z0 


280 


fe 


240 


200 


160 


120 


80 


40 


''When  one  straiglitens  up  after  a  ean.'ful  microscopic  examina- 
tion of  the  pattern  of  Diahroiica  to  determine  its  variation,  one 
is  sure  that  no  other  enemy  of  these  tiower  beetles  can  be  conceived 
to  use  such  discrimination  as  ours.  Does  the  fly  catcher  swooj)- 
ing  from  its  station  on  fence  post  or  tree  branch  determine  which 
of  two  heavily  flying  Dia- 
broticas  shall  be  its  prey  on 
the  basis  of  'two  middle 
spots  on  left  elytron  partial- 
ly fused'  in  one  and  'these 
two  spots  not  touching'  in 
the  other?  To  our  minds 
the  change  in  variation 
status,  the  dominance  of  one 
mode  to-day  which  was  the 
subordinate  mode  in  1895, 
is  not  due  to  the  action  of 
selection.  We  do  not  indeed 
hesitate  to  believe  in  those 
'unknown  factors  of  evolu- 
tion' which  may  produce, 
among  other  results,  that 
condition  of  affairs  best 
named  '  determinate  varia- 
tion.' This  variation  is  not 
necessarily  to  be  conceived 
of  as  purposeful  or  even 
advantageous  ;  if  by  its 
cumulation  it  becomes  a 
disadvantage  of  life  -  and  - 
death  value,  natural  selec- 
tion, which  is  after  all  a 
logical  necessity  and  un- 
doubtedly an  actual  actively  regulative  factor  in  species  control;  will 
take  care  of  it." 


Classes;;!;; 

V^ndtes3l3  32 


60 


MlSCEl 


Hi:-: 

396  B04tofal905 


Fig.  91. — Frequency  polygon  of  variation  of 
elytral  pattern  in  905  specimens  of  the  Cali- 
fornia flower  beetle,  Diabrotica  soior,  col- 
lected at  Stanforil  University,  October,  1901. 
(After  Kellogg  and  Bell.) 


In  the  light  of  the  foregoing  discussion  of  the  oatogories  and 
characters  of  variations,  it  is  obvious  that  a  well-grounded 
knowledge  of  variability  and  variations,  a  knowledge  based  on 
careful  extensive  statistical  and  exjierimental  studies,  is  essen- 
tial as  a  basis  for  anv  effective  investigation  of  the  factors  and 


154 


EVOLUTION   AND   ANIMAL   LIFE 


360 


3Z0 


m 


240 


200 


160 


120 


80 


40 


processes  involved  in  species-forming,  that  is,  evolution.  The 
methods  and  phenomena  of  evolution  are  intimately  linked 
with — indeed  throughout  are  based  upon — the  methods  and 
phenomena  of  variation.  What  causes  variation  is  a  contrib- 
utory cause  in  evolution, 
and  one  of  the  funda- 
mental and  all-important 
causes. 

Concerning  the  causes 
of  variation,  at  least  of 
those  of  congenital  varia- 
tion, we  are  almost  wholly 
in  the  dark.  Only  such 
influences  as  can  affect 
the  actual  germ  cells  are 
presumably  potent  to  ef- 
fect congenital  variation. 
Such  influences  are  not 
proved  to  the  satisfac- 
tion of  many  biologists 
to  be  numerous.  In  the 
fusion  of  the  germ  cells 
of  two  individuals,  the 
phenomenon  called  by 
him  amphimixis,  Weis- 
mann  finds  the  most  ef- 
fective cause  of  variation. 
Now  the  wider  apart  the 
two  parents  are  in  struc- 
tural and  functional  char- 
acteristics, the  greater  is 
the  variation  in  their  off- 
spring likely  to  be.  Hence  hj^bridization,  or  the  mating  of 
unlike  parents,  even  to  the  degree  of  race  and  species  un- 
likeness,  is  a  great  resource  of  the  breeder  who  would  have  in 
his  hands  large  variation.  But  if  the  parents  are  too  unlike, 
their  mating,  even  if  possible,  proves  sterile.  Llsually  parents 
must  be  of  the  same  species,  although  experiment  has  shown 
that  considerable  extraspecific  hybridization  is  possible.  Among 
cultivated  plants  and  animals  the  artificially  selected  races 
differ  vei-y  mucli,  but  these  races  are  mostly  easily  hybridiz- 


Classes::": 
Variates  3l3   40 


55 


388 


miscfl' 

09  total  905 


Fig.  92. — ^Frequency  polygon  of  variation  of 
elytral  pattern  in  905  specimens  of  the  Cali- 
fornia flower  beetle,  Diabrotica  soror,  col- 
lected at  Stanford  University,  October,  1902. 
(After  Kellogg  and  Bell.) 


VARIATION   AND   MUTATION 


155 


able.     The  nature  and  results  of  fertilization  and  ajuphiinixis 
are  treated  in  Chapter  XIII. 

But  parthenogenetically  produced  individuals  (that  is, 
young  born  from  unfertilized  eggs — as  the  honey-bee  drones, 
certain  wliole  generations  of  various  gall  flies,  saw  flies,  ai)hids, 
etc.,  etc.,  regularly  are)  also  vary. 
In  the  case  of  male  bees,  male 
ants,  female  aphids,  etc.,  etc.,  the 
individuals  differ  quite  as  much  as 
do  individuals  of  the  same  species 
of  bisexual  parentage.  Comparing 
the  variation  in  drone  bees  (par- 
thenogenetically produced)  as  com- 
pared with  that  of  the  workers 
(from  fertilized  eggs),  we  find  that 
this  is  true.  The  organs  examined 
for  variation  in  these  series  of  bees  were  the  wings,  organs 
used  by  both  drones  and  workers,  and  having  no  immedi- 
ate relation  either  structurally  or  physiologically  to  the  differ- 
entiation of  those  two  castes  or  kinds  of  individuals  of  the 
honey-bee  species.  The  workers  are  "  incomplete  "  only  in  that 
most  of  them  are  infertile:  in  no  other  structural  or  physiological 
feature  of  their  makeup  are  they  less  "complete"  than  the 
drones.     They  are  indeed  distinctly  the  more  speciahzed    of 


Fig.  93. — Fore  and  hind  wings 
of  honeybee  (drone),  sliowinj? 
normal  venation.  (After  Kel- 
logg and  Bell.) 


Fig.  94. — ^Part  of  costal  margin  of  hind  wing  of  honeybee,  much  magnified  to  show 

hooks.      (After  Kellogg  and  Bell.) 


the  two,  and  according  to  one  of  the  early  Darwinian  canons  of 
variation  might  be  expected  to  differ  more  than  the  drones. 
But  the  drones  are  males  and,  according  to  another  commonly 
accepted  belief,  this  is  the  explanation  for  a  larger  variation  on 
their  part,  if  such  larger  variation  occurs.  As  a  matter  of  fact, 
it  does.  The  drones,  in  all  the  many  series  studied,  sliow  mark- 
edly more  variation  in  the  venation  of  the  wings  than  do  the 
workers,  while  they  show  quite  as  nnich  variation  as  the  work- 
ers in  the  number  of  the  hooks  which  liold  the  two  wings  togetlier 
in  flight.  (See  Figs.  93  to  96.)  Botli  these  characters,  i.e., 
wing  venation  and  wing  hooks,  are  not  so-called  "  male  diar- 


156 


EVOLUTIOX   AND   ANIMAL   LIFE 


acters":  they  are  not  to  be  compared  with  those  secondary 
sexual  characters  such  as  ornamental  or  aggressive  spines, 
horns,  patterns,  etc.,  which  are  the  characteristics  that  give 
males  their  special  reputation  for  ultra  variation. 


Fig.  95. — Fore  wings  of  honej'^bee  (drone) ,  showing  variations  in  venation. 

(After  Kellogg  and  Bell.) 

Finally,  with  regard  to  the  causal  influence  in  variation-pro- 
ducing of  the  "primary  factors  of  evolution,^'  such  as  temper- 
ature, hght,  humidity,  pressure,  and  extrinsic  physicochemical 
conditions  generally,  summed  up  commonly  in  the  phrase 
chmate  and  environment,  we  have  one  all-important  considera- 
tion to  keep  constantly 
in  mind.  However  po- 
tent and  obvious  the  ef- 
fects of  these  influences 
are  on  the  individual, 
we  have  no  proof  as 
yet  of  a  nature  to  com- 
pel the  general  accept- 
ance of  biologists,  that 
such  effects  can  be  car- 
ried directly  over  to  the 
race  or  species. 

Only  ten  years  after 
Darwin  published  the 
"Origin  of  Species,^^  von  Kolliker,  the  great  German  zoologist, 
in  criticising  the  assumptions  on  which  species-forming  by 
natural  selection  was  based  in  the  Darwinian  theory,  proposed 
an  alternative  theory  of  heterogenesis  or  species-forming  by 
leaps  (saltations  or  mutations).  These  saltations  need  not  of 
necessity  to  be  large,  but  must  be  changes  definite  and  fixed. 
Later,  Korschinsky,  a  Russian  botanist,  outhned  in  some  de- 


FiG.  96. — Hind  wings  of  honeybee  (drone),  show- 
ing variations  in  venation.  Note  the  interpola- 
tion of  the  cells.     (After  Kellogg  and  Bell.) 


VARIATION   AND   MITATION  157 

tail  and  with  greater  empliayis  such  a  theory  of  specios-forin- 
ing  by  mutations;  and  finaUy  in  1901  Hugo  de  Vrics,  the 
famous  botanist  of  Amsterdam,  pul)hshed  in  cxtenso  the  details 
of  many  years  of  observation  and  experiment  on  the  subject  of 
mutations,  and  reformulated  definitively  a  theory  of  species- 
forming  by  mutational  or  saltational  variation,  the  now  famil- 
iar mutation  theorv. 

The  following  paragraphs  from  Morgan  ("Evolution  and 
Adaptation,''  \)\).  294-297,  1903)  give  a  concise  statement  of 
the  actual  details  of  the  mutations  in  the  evening  primrose  ob- 
served by  de  Vries : 

"We  may  now  proceed  to  examine  the  evidence  from  which  tic 
Vries  has  been  led  to  the  general  conclusions  given  in  the  prece(lin«; 
])ages.  De  Vries,  found  at  Hilversam,  near  Amsterdam,  a  locality 
wliere  a  number  of  plants  of  the  evening  primrose,  Oenothera  lamarvh- 
iana,  grow  in  large  numbers.  This  plant  is  an  American  form  that 
has  been  imported  into  Europe.  It  often  escapes  from  cultivation,  as 
s  the  case  at  Hilversam,  where  for  ten  years  it  had  been  growing 
wild.  Its  rapid  increase  in  numbers  in  the  course  of  a  few  years  may 
be  one  of  the  causes  that  have  led  to  the  appearance  of  a  mutation 
period.  The  escaped  plants  showed  fluctuating  variations  in  r.carly 
all  of  their  organs.  They  also  had  produced  a  number  of  abnoi-mal 
forms.  Some  of  the  plants  came  to  maturity  in  one  year,  others  in 
two,  or  in  rare  cases  in  three,  years. 

"A  year  after  the  first  finding  of  these  plants  de  Vries  observed 
two  well-characterized  forms,  which  he  at  once  recognized  as  new 
elementary  species.  One  of  these  was  0.  breristj/h's,  which  occurred 
only  as  female  plants.  The  other  new  species  was  a  smooth-leafed 
form  with  a  more  beautiful  foliage  than  0.  lamarckiana.  This  is  0. 
Icevifolia.  It  was  found  that  both  of  these  new  forms  bred  true  from 
self-fertilized  seeds.  At  first  only  a  few  specimens  were  found,  each 
form  in  a  particular  part  of  the  field,  which  looks  as  though  each  miglit 
have  come  from  the  seeds  of  a  single  plant. 

"These  two  new  forms,  as  well  as  the  common  0.  hnnarckiana, 
were  collected,  and  from  these  i)lants  there  have  arisen  the  three 
groups  or  families  of  elementary  species  that  de  Vrics  ]ia.s  studied. 
In  his  garden  other  new  forms  also  arose  from  those  that  had  Imhmi 
brought  under  cultivation.  The  hvgest  grou|).  and  the  most  impor- 
tant one,  is  that  from  the  oiiginal  (K  lumarckiaiKi  form.  The  accom- 
panying table  shows  the  mutation.^  that  arose  between  1SS7  and  ISDO 


158 


EVOLUTION  AND  ANIMAL  LIFE 


from  these  plants.  The  seeds  were  selected  in  each  case  from  self- 
fertilized  plants  of  the  lamarckiana  form,  so  that  the  new  plants  ap- 
pearing in  each  horizontal  line  are  the  descendants  in  each  generation 
of  lamarckiana  parents.  It  will  be  observed  that  the  species,  0.  ob- 
longata, appeared  again  and  again  in  considerable  numbers,  and  the 
same  is  true  for  several  of  the  other  forms  also.  Only  the  two  species, 
0.  gigas  and  0.  sciritillans,  appeared  very  rarely. 

"(ENOTHERA  LAMARCKIANA 

Elementary  Species 


r"™  „     Aiuvi„    Obion-    Rubri-   Lamarck-    Nan-     t„.  Scin- 

Gigas.  Albida.    ^^^^       ^^^.^j^         -^^^         ^^^^^      Lata.    ^-^^^^^^ 


Generation. 

8  Gener 
VIIL      1899 
annual 


0 


1,700      21 

V 


7  Gener 
VII.      1898 
annual 


0 3,000 11 


V 


6  Gener 
VI.      1897 
annual 


11         29 


1,800         9 


5  Gener 
V.      1896 
annual 


25       135 


20 


8,000      49      142 

— V 


6 


4  Gener 
IV.      1895 
annual 


15       176 


8        14,000      60        73 
V 


3  Gener 

III.  .1890-91 

biennial 


1 10,000        3  3 

V 


2  Gener 

11.    1888-89 

biennial 


15,000         5  5 

V 


1  Gener 

I.    1886-87 

biennial 


9 


"Thus  de  Vries  had,  in  his  seven  generations,  about  fifty  thousand 
plants,  and  about  eight  hundred  of  these  were  mutations.  When  the 
flowers  of  the  new  forms  were  artificially  fertilized  with  pollen  from 


VARIATION  AND  MUTATION 


159 


the  flowers  on  the  same  plant,  or  of  the  same  kind  of  phuit,  they  gave 
rise  to  forms  hke  themselves,  thus  showing  that  they  are  true  elemen- 
tary species.'  It  is  also  a  point  of  some  interest  to  observe  that  all 
these  forms  differed  from  each  other  in  a  large  number  of  particulars. 
"Only  one  form,  0.  scintillans,  that  appeared  eight  times,  is  not 
constant  as  are  the  other  species.     When  self-fertilized,  its  seeds  pro- 


FiG.  97. — At  left,  section  of  chestnut,  Castanea  vesca,  showing  unusual  variations;  at 
right,  a  branch  of  Mercurialis  annua,  which  presents  several  variations,  (.\fter 
de  Vries.) 


duce  always  three  other  forms,  0.  scintillnnfi,  0.  ohhngata,  and  0. 
lamarckiana.  It  differs  in  this  respect  from  all  the  other  elementary 
species,  which  mutate  not  more  than  once  in  ten  thousand  individuals. 
From  the  seeds  of  one  of  the  new  forms,  0.  Urrijolia,  collected  in 
the  field,  plants  were  reared,  some  of  which  were  (K  lamarckiana,  and 
others  0.  Icevifolia.  They  were  allowed  to  grow  together,  and  their 
descendants  gave  rise  to  the  same  forms  found  in  the  lamarckiana 

'  0.  lata  is  always  female,  and  cannot,  therefore,  1h'  sclf-fcrtiliztHl. 
When  crossed  with  0.  lamarckiana  there  is  produced  fifteen  to  twenty  per 
cent  of  pure  lata  individuals. 


160 


EVOLUTION  AND  ANIMAL  LIFE 


family,   described  above,  nameh^,  0.  lata,  cUipiica,  nannella,  ruhri- 
nervis,  and  also  two  new  species^  0.  spatulcda  and  leptocarpa. 

"In  the  lata  family,  only 
female  flowers  are  produced,  and, 
therefore,  in  order  to  obtain  seeds 
they  were  fertilized  with  pollen 
from  other  species.  Here  also  ap- 
peared some  of  the  new  species, 
already  mentioned,  namely,  aU 
bida,  nannella,  lata,  oblongata,  ru- 
brinei'vis,  and  also  two  new  species, 
elliptica  and  subovata. 

"De  Vries  also  watched  the 
field  from  which  the  original  forms 
were  obtained,  and  found  there 
many  of  the  new  species  that  ap- 
peared under  cultivation.  These 
were  found,  however,  only  as 
weak  young  plants  that  rarely 
flowered.  Five  of  the  new  forms 
were  seen  either  in  the  Hilversam  field,  or  else  raised  from  seeds  that 
had  been  collected  there.  These  facts  show  that  the  new  species  are 
not  due  to  cultivation,  and  that  they  arise  year  after  year  from  the 
seeds  of  the  parent  form,  0.  lamarckiana." 


Fig.  98. — Stamens  of  a  hybrid  willow, 
Salix  auritax  purpurea,  showing  dif- 
ferent degrees  of  varying. 


Fig.  99. — ^A  branch  of  a  Japanese  tree,  Cryptomeria  japonica,  showing  an  atavistic 

variation.     (After  de  Vries.) 


As  to  this  we  may  observe:     It  has  long  been  known  that 
hidividual  vr.riations  of  an  extreme  degree  sometimes  occm*. 


VARIATION   AND   MUTATION 


IGl 


and  that  these  may  be  to  a  degree  persistent  in  heredity.  Of 
such  nature  was  the  Ancon  sheep,  the  Mauchamp  sheep,  the 
iceberg  blackberry,  and  numerous  other  races  or  forms  known  in 
the  domestication  of  animals,  or  the  cultivation  of  plants.  The 
generally  normal  str-uctm-e  of  such   individuals  distinguishes 


Fig.  100. — A  branch  of  the  green  Georgine,  in  which  the  inflorescence  leaves  and  some 
of  one  branch  (the  right-hand  one)  are  green  hke  the  rest  of  the  plant,  while  the 
other  varieties  are  red  and  in  normal  condition.     (After  de  Vries.) 


them  from  monstrosities,  which  are  usually  freaks  of  develop- 
ment rather  than  of  heredity. 

The  name  "saltation,"  or  in  recent  years  ''mutation,"*  has 
been  applied  to  extreme  fluctuation,  the  immediate  cause  of 
which  is  unknown.  The  experiments  of  de  Vries  on  the  salta- 
tions of  the  descendants  of  the  evening  primrose  (called  (l^no- 
thera  lamarckiana)  have  dra"v\Ti  general  attention  again  to  the 
possibility  that  saltation  has  had  a  large  part  in  the  process  of 

'  The  word  mutation  was  first  used  not  for  saltations  but  for  the  slow 
fluctuatioft  ijti  successive  geologicg-l  periods. 


162  EVOLUTION   AND   ANIMAL   LIFE 

formation  of  species.  As  to  this  it  may  be  said  that  the  possible 
variation  within  each  species  is  much  greater  than  the  range 
of  the  individuals  which  actually  survive.  The  condition  of 
domestication  favors  the  development  of  extreme  variation,  be- 
cause such  individuals  may  be  preserved  from  interbreeding 
with  the  mass,  and  they  may  survive  even  if  their  characters 
are  unfavorable  to  competition  in  the  struggle  for  existence. 
Among  plants  it  is  noticed  that  new  soil  and  new  conditions 
seem  to  favor  large  variation  in  the  progeny,  although  the  traits 
thus  produced  are  not  usually  hereditary.  Cases  more  or  less 
analogous  to  those  noted  by  Dr.  de  Vries  are  not  rare  in  horti- 
culture. The  cross  breeding  of  variant  forms  favors  the  ap- 
pearance of  new  forms.  Among  actual  species  in  a  state  of 
nature,  there  are  very  few  which  seem  likely  to  have  arisen  by  a 
sudden  leap  or  mutation.  The  past  and  the  future  of  de  Vries' 
evening  primroses  are  yet  to  be  shown.  The  species  called  by 
de  Vries  Oenothera  lamarckiana  is  not  at  present  known  in  its 
wild  state  anywhere  in  North  America,  the  parent  region  of  all 
the  species  of  evening  primroses  or  Oenothera;  so  that  we  have 
as  yet  no  reason  to  assume  that  the  various  mutants  of  the 
evening  primrose  are  really  comparable  to  the  wild  species  of 
the  same  group  now  existing  in  America. 

While  saltation  remains  as  one  of  the  probable  sources  of 
specific  difference,  the  actual  role  of  this  process  in  nature  is 
yet  to  be  proved. 


C!. 


CHAPTER  X 
HEREDITY 

Vom  Vater  hab'  ieh  die  Statur, 

Des  Lebens  ernstes  Fiihren; 
Vom  Miitterchen  die  Frohiiatur 

Und  Lust  zu  fabuliren. 

Urahnherr  war  der  Schonsten  hold, 

Das  spukt  so  hin  und  wieder. 
Urahnfrau  liebte  Sehmuck  und  Gold, 

Das  zuckt  wohl  durch  die  Glieder. 

Sind  nun  die  Elemente  nicht 

An  dem  Complex  zu  trennen; 
Was  ist  denn  an  dem  ganzen  Wicht 

Original  zu  nennen?" 

— Goethe,  ^  "  Zahme  Xenien,"  vi. 

Heredity  is  the  rule  of  persistence  among  organisms.  The 
existence  of  such  a  law,  or  "ascertained  sequence  of  events,"  is 
a    matter    of    common    observation.     "Like    produces    like," 

^  "Stature  from  father  and  the  mood 
Stem  views  of  life  compelling; 
From  mother,  I  take  the  joyous  heart 
And  the  love  of  story-telling. 

"Great-grandsire's  passion  was  the  fair. 
AVhat  if  I  still  reveal  it? 
Great-grandam's,  pomp  and  gold  and  show, 
And  in  my  bones  I  feel  it. 

"Of  all  the  various  elements 

That  make  up  this  conipk'xity, 
What  is  there  left  when  all  is  done, 
To  call  originality?  " 

Bayahd  Tayloh's  translation  in  jxirt. 

163 


164  EVOLUTION  AND  ANIMAL  LIFE 

"Blood  will  tell/'  "Blood  is  thicker  than  water/'  these  proverbs 
in  all  languages  indicate  the  general  fact  that  each  organism  is 
likely  to  resemble  its  parents,  and  that  the  basis  of  fmidamental 
resemblance  among  organisms  is  found  in  kinship  by  blood.  It 
is  equally  a  matter  of  common  observation  that  the  law  of  hered- 
ity is  inseparable  from  a  law  of  variation.  No  one  organism  is 
quite  an  exact  copy  of  another.  The  prevention  of  such  a  con- 
dition is  one  of  the  effects  of  the  process  of  double  parentage. 
Except  in  certain  exceptional  forms  in  w^hich  parthenogenesis 
or  hermaphroditism  appear,  each  complex  organism  springs 
from  two  organisms  of  the  same  species:  the  one  male,  the  other 
female.  The  resultant  organism  partakes  of  the  qualities  of 
each  of  these  in  some  degree,  and  through  these  to  a  degree  also 
it  partakes  of  qualities  of  the  parents  or  ancestors  of  each. 

The  phrase,  "Kinship  by  blood,"  used  in  connection  with  all 
studies  of  heredity,  is  a  survival  of  an  ancient  theory  that  the 
physical  basis  of  heredity  is  found  in  the  actual  blood.  "  Blood 
is  quite  a  peculiar  juice,"  as  was  observed  by  Mephistopheles, 
but  its  peculiarities  are  not  concerned  with  heredity.  The  func- 
tion of  blood  is  concerned  with  the  nourishment  of  tissues  and 
the  removal  of  their  waste.  The  actual  vehicle  of  transfer  of 
hereditary  qualities,  the  physical  basis  of  heredity,  is  found  in 
structures  within  the  protoplasm  of  the  germ  cell. 

The  germ  cells,  male  or  female,  are  alike  in  all  characters 
essential  to  this  discussion.  On  the  average,  the  potency  of  the 
male  and  the  female  cell  is  exactly  the  same,  there  being  nowhere 
constant  advantage  of  one  sex  over  the  other.  Each  cell,  male 
or  female,  is  one  of  the  vital  units,  or  body  cells, -set  apart  for 
the  special  purpose  of  reproduction.  It  is  not  essentially  differ- 
ent from  other  cells  in  structure  or  in  origin,  but  in  its  poten- 
tialities. Its  function  is  that  of  repeating  the  original  organism, 
"  with  the  precision  of  a  w^ork  of  art." 

Heredity  is  shown  in  the  persistence  of  type,  in  the  existence 
of  broad  homologies  among  living  forms,  in  the  possibility  of 
natural  systems  of  classification  in  any  group,  in  the  retention 
of  vestigial  organs,  in  the  early  development  and  subsequent 
obliteration  of  outworn  structures  once  useful  to  individuals  of 
the  race  or  type. 

In  a  general  way,  the  individual  inherits  from  both  parents 
the  common  structure  of  organisms  of  the  species  to  which  it 
belongs.     The  special  peculiarities  of  the  individual  organism 


HEREDITY  165 

are  also  inherited,  but  in  much  Jess  certainty  of  degree.  These 
traits  belonging  to  a  member  of  a  single  generation  have  a 
smaller  "inheritance  fund"  on  which  to  draw.  In  each  gener- 
ation some  of  these  individual  qualities  are  latent  or  "reces- 
sive," others  are  potent  or  "dominant."  The  recessive  or  an- 
cestral characters  reappear  with  a  certain  regularity.  They 
may  form  a  sort  of  mosaic,  by  mixing  with  other  dominant 
traits,  or  they  may  make  a  more  or  less  perfect  blend.  Resem- 
blance to  some  remote  ancestor  occurs  at  times,  being  known  as 
atavism.  Each  ancestor  has  some  claim  in  the  formation  of  the 
new  individual,  and  behind  the  grandfather  and  grandmother 
dead  hands  from  older  graves  reach  in  their  direction.  The  past 
will  never  let  go,  though  with  each  generation  there  is  a  deeper 
crust  over  it.  These  old  claims  grow  less  with  time,  because 
with  each  new  generation  there  are  twice  as  many  of  these  com- 
petitors. ^Moreover  past  generations  can  afTect  the  heredity 
of  the  individual  only  through  the  agency  of  his  immediate 
parents.  Out  of  these  elements  Mr.  Galton  frames  the  idea  of  a 
"  mid-parent,"  a  sort  of  center  of  gravity  of  heredity,  though,  as 
Dr.  Brooks  has  observed,  it  is  doubtful  if  this  mid-parent  is 
more  than  a  logical  abstraction.  The  bluer  the  blood  in  any 
species,  that  is,  the  more  closely  alike  the  ancestors  are,  the 
more  certain  will  be  the  personal  resemblance  among  the  de- 
scendants. 

But  characters  actually  latent  are  very  real  in  heredity. 
Dr.  Brooks  says : 

"When  a  son  of  a  beardless  boy  grows  up  and  acquires  a  heard,  we 
may  say  that  he  has  inherited  his  grandfather's  beard,  but  this  is  only 
a  figure  of  speech,  and  he  actually  inherits  the  beard  his  father  miglit 
have  acquired,  had  he  lived,  nor  would  the  case  of  a  child  descended 
from  a  series  of  ten  or  a  hundred  beardless  boys  be  different." 

It  is,  moreover,  certainly  true  that  a  beard  can  be  as  well 
inherited  from  the  mother — who  has  none — as  from  the  father. 
The  inheritance  is  that  of  the  beard  the  mother  might  have 
developed  had  she  been  a  man.  And,  in  general,  in  matters  of 
heredity,  the  child  is  not  derived  from  the  parents  as  they 
actually  are,  but  from  tlie  parents  as  they  might  liave  been. 
The  traits  transmitted  in  heredity  are  chosen  from  the  whoh'  hue 
of  parental  possibilities.  And  with  the  process  of  conception, 
12 


166  EVOLUTION  AND  ANIMAL  LIFE 

the  union  of  the  two  parental  germ  cells,  "the  gate  of  gifts  is 
closed."  No  trait  or  quality  can  ever  be  acquired  of  which  at 
least  the  elements  are  not  involved  in  the  original  inheritance. 

"What  is  transmitted  to  the  infant,"  observes  Dr.  Archdall 
Reid,  "is  not  the  modification  [of  the  parent],  but  only  the 
power  of  acquiring  it  under  similar  circumstances.  The  power 
to  acquire  fit  modifications  in  response  to  appropriate  stimula- 
tion is  that  vv^hich  especially  differentiates  high  animal  organ- 
isms from  low  animal  organisms." 

Atavism  or  reversion  is  the  process  of  "throwing  back,"  by 
which  in  some  degree  an  individual  resembles  a  distant  ancestor. 
Under  the  name  of  "atavism,"  according  to  Yves  Delage,  are 
included  three  very  different  things: 

(a)  The  transmission  in  one  family  of  indi\ddual  characters, 
which,  latent  for  several  generations,  suddenly  reappear.  This 
is  family  atavism,  and  its  nature  is  readily  recognized. 

(b)  The  reappearance,  more  or  less  regularly  in  a  race,  of 
characters  of  an  allied  race,  from  which  the  first  race  may  have 
been  derived.  This  is  race  atavism.  Of  this  nature  are  the 
zebra  stripes  sometimes  seen  in  mules. 

(c)  The  appearance  of  characters  abnormal  for  the  race  in 
which  they  appear,  but  which  are  normal  in  other  races  sup- 
posed to  be  ancestral.  This  is  atavism  of  teratology.  An  illus- 
tration is  the  occasional  appearance  in  the  modern  horse  of  rudi- 
ments of  additional  toes,  with  partly  developed  hoofs. 

"Everything  is  possible  in  heredity,"  observes  Delage. 
"One  may  always  find  examples  of  election,  of  blending  (of 
mosaic),  of  combination,  of  resemblance  direct,  and  of  resem- 
blance reversed.  To  give  to  these  groupings  the  name  of  laws 
would  be  an  abuse  of  language,  since  not  one  of  these  rules  is 
exclusively  true.  In  reality  there  is  no  law  of  resemblance  be- 
tween a  child  and  its  parents.  All  is  possible,  from  a  difference 
so  great  that  there  is  not  a  trait  in  common,  to  an  almost  perfect 
identity  with  one  or  the  other  parent,  with  every  intermediate 
degree  of  blending  of  characters  and  combination  of  resem- 
blances." 

The  name  "  telegony  "  is  given  to  the  supposed  influence  of 
the  first  male  on  the  future  offspring  of  the  female.  This  theory 
of  telegony  rests  mainly  on  a  case  of  a  mare  which  was  first  im- 
pregnated by  a  quagga,  and  whose  subsequent  colts  from  males 
of  her  own  species  had  quagga-like  markings.     The  supposed 


HEREDITY  107 

facts  on  which  the  theory  is  based  are  inadequate  or  iinjiroved, 
and  it  is  probable  that  the  phenomena  called  telegony  have  no 
real  existence. 

Equally  uncertain  are  the  phenomena  known  as  "})renatal 
influences.'^  In  the  process  of  evolution,  the  development  of  I  Ik; 
female  has  brought  her  to  be  more  and  more  the  protector  and 
helper  of  the  young.  She  gives  to  her  progeny  not  only  her 
share  of  its  heredity,  but  she  becomes  more  and  more  a  factor  in 
its  development.  In  the  mammalia  the  little  egg  is  retained 
long  in  the  body  and  fed,  not  with  food  yolk,  but  with  tlie 
mother's  blood.  The  parent  thus  becomes  an  immediate  and 
most  important  part  of  the  environment  of  the  young.  In  man, 
by  the  growth  of  the  family  the  parental  environment  Ijecomes 
a  lifelong  influence.  The  father  as  well  as  the  mother  becomes  a 
part  of  it. 

It  has  long  been  a  matter  of  common  behef  that  among 
mammals  a  special  additional  formative  influence  is  exerted  by 
the  mother  in  the  period  between  conception  and  birth.  Tlie 
patriarch  Jacob  is  recorded  as  having  made  a  thrifty  use  of  this 
influence  in  relation  to  the  herds  of  his  father-in-law,  Laban. 
This  belief  is  part  of  the  folklore  of  almost  every  race  of  intelli- 
gent men.  In  the  translations  of  Carmen  Silva,  that  gentle 
woman  whom  kind  nature  made  a  poet  and  cruel  fortune  a 
queen,  we  find  these  words  of  a  Roumanian  peasant  woman : 

"My  little  child  is  lying  in  the  grass, 
His  face  is  covered  with  the  blades  of  grass. 
While  I  did  bear  the  child,  I  ever  watched 
The  reaper  work,  that  it  might  love  the  harvests; 
And  when  the  boy  was  born,  the  meadow  said, 
'This  is  my  child.'" 

In  the  current  literature  of  hysterical  ethics  we  find  all  sorts 
of  exhortations  to  mothers  to  do  this  and  not  to  do  that,  to 
cherish  this  and  avoid  that  on  account  of  its  supposed  effect 
on  the  coming  progeny.  Long  lists  of  cases  have  been  rei>ort(Ml 
illustrating  the  law  of  prenatal  influence.  Most  of  these  records 
serve  only  to  induce  scepticism.  Many  of  these  are  mere  co- 
incidences, some  are  unverifiable,  others  grossly  imi)ossil)le. 
There  is  an  evident  desire  to  make  a  case  rather  than  to  tell  the 
truth.     The  whole  matter  is  much  in  need  of  serious  study,  and 


168  EVOLUTION   AND  ANIMAL   LIFE 

the  entire  record  of  alleged  facts  must  be  set  aside  to  make  a 
fair  beginning. 

There  are  also  many  phenomena  of  transmitted  qualities 
that  cannot  be  charged  to  heredity.  Just  as  a  sound  mind  de- 
mands a  sound  body,  so  does  a  sound  child  demand  a  sound 
mother.  Bad  nutrition  before  as  well  as  after  birth  may  neu- 
tralize the  most  vigorous  inheritance  within  the  germ  cell.  A 
child  Avell  conceived  may  yet  be  stunted  in  development.  Even 
the  father  may  transmit  weakness  in  development  as  a  handicap 
to  hereditary  strength.  The  many  physical  vicissitudes  between 
conception  and  birth  may  determine  the  rate  of  early  growth 
or  the  impetus  of  early  development.  In  a  sense,  the  im- 
pulse of  life  comes  from  such  sources  outside  the  germ  cell 
and  outside  heredity.  All  powers  may  be  affected  by  it.  Per- 
fect development  demands  the  highest  nutrition,  an  ideal 
never  reached.  In  such  fashion  the  child  ma}^  bear  the  in- 
cubus of  Ibsen's  "Ghosts,'' for  which  it  had  no  personal  re- 
sponsibility. "  Spent  passions  and  vanished  sins  "  may  impair 
germ  cells,  male  or  female,  as  they  injure  the  organs  that 
produce  them. 

In  a  thoughtful  article  on  problems  of  heredity  {The  Horse- 
man, April  17,  1906),  Mr.  C.  B.  Whitford  maintains  that  better 
results  in  the  trotting  horse  come  from  breeding  from  untrained 
horses  of  good  blood  than  from  horses  which  have  been  elabo- 
rately trained  to  the  highest  speed  on  the  racecourse. 

"Trotting  horses  that  are  overbred  show  the  effects  of  their  inten- 
sified breeding  in  a  variety  of  ways.  But  the  usual  diliiculty  is  ex- 
treme nervousness  and  want  of  ability  to  stand  training.  Sometimes 
a  horse  of  this  Idnd  ^vill  show  great  jDromise  when  he  is  first  hitched  to 
a  sulky.  He  ^\\\\  show  great  flashes  of  speed  and  will  have  a  smooth, 
easy  action  and  the  trotting  instinct  well  pronounced." 

But  he  is  overnervous,  lacks  constitutional  strength  and  will 
not  do  well. 

"The  trouble  with  a  horse  of  this  Idnd  is  that  he  has  not  inherited 
the  necessary  fuel  with  which  to  create  energy.  He  is  'burnt  out' 
by  heredity.  Tliat  which  he  needed  to  train  on  was  so  largely  used 
up  by  his  ancestry  in  their  process  of  development  that  they  had  not 
enough  to  transmit  to  their  progeny." 


HEREDITY 


169 


Fig.  101. — Diagram  showing  arrangement  of  hones  in  the  hantl  or  foot 
of  various  animals  :  1 ,  man  ;  2,  gorilla  ;  3,  orang  ;  4.  dog  ;  f),  sea  lion  ;  G, 
dolphin;  7,  bat;  8,  mole;  9,  Ornithorhynchus.     (After  Haeckel.) 


170 


EVOLUTION   AND  ANIMAL  LIFE 


If  this  is  true,  it  would  appear  that  nervous  overstrain  of 
the  parent  is  unfavorable  to  normal  nerve  development  of  the 
offspring.  This  would  be  apparently  a  case  of  transmission  of 
parental  conditions,  as  above  indicated,  and  not  one  of  true 
heredity. 

It  may  be  conceived  that,  at  the  moment  of  impregnation, 
the  resultant  germ  cell  is  sexless.  It  begins  its  development  at 
once,  and,  in  the  higher  animals,  turns  very  soon  toward  the 
formation  of  those  structures  which  distinguish  the  one  sex  or 
the  other.  Each  individual  ultimately  becomes  either  male  or 
female.     Relatively  few  animals,  and  those  among  the  lower 


Fig.  102. — Limb  skeletons  of  extinct  and  living  animals,  showing  the  homologous 
bones:  1,  salamander;  2,  frog;  3,  turtle;  4,  Aetosaurus;  5,  Plesiosaurus;  6,  Ichthyo- 
saurus; 7,  Mososaurus;  8,  duck. 


forms,  are  ever  really  hermaphrodite,  or  representative  of  both 
sexes  at  once. 

Among  the  invertebrate  animals  the  numerical  relations  of 
the  sexes  are  subject  to  great  variation.  Among  vertebrates, 
in  general,  the  sexes  are  practically  equal  in  number,  as  is  shown 
by  count  of  large  series  of  individuals.  This  is  true  whether  the 
species  be  monogamous,  polygamous,  or  promiscuous  in  its  sex 
relations.     It  is  therefore  apparent  that  the  sex  tendencies  in 


HEREDITY 


171 


the  germ  are  held  on  a  very  fine  bahxnce.  A  very  shf^lit  impulse 
the  one  way  or  the  other  determines  the  sex  direction  tlie  em- 
bryo shall  take.  Although  much  investigation  and  very  nuich 
speculation  have  been  devoted  to  tliis  problem,  it  is  still '  un- 
solved. We  are  not  able,  in  the  vertebrate  animals,  nor  in  fact 
in  animals  generally,  to  determine  the  nature  of  the  stinuilus,  or 
of  any  of  the  various  impulses,  if  more  than  one  exists,  which 


m 


Fig.  103. — Limb  skeletons  of  various  animals,  showing  homologous  bones:  9.  Orni- 
thorhynchus;  10,  kangaroo;  11,  Megatherium;  12,  armadillo;  13,  mole;  14,  sea 
lion;  15,  gorilla;  16,  man. 

leads  the  individual  germ  cell  to  develop  as  male  or  female. 
It  is  also  possi])le  that  each  germ  cell  is  really  bisexual  from  the 
beginning.  One  sex  .or  the  other  liecomes  dominant  and  the 
other  recessive  as  the  embryo  develops.  But  in  this  event  wr 
are  still  in  doubt  as  to  the  nature  of  the  determining  factor  oi- 

^  The  latest  studios  of  (ho  prohlom  aro  rliiofly  ronooriiod  with  an  attompt 
to  dotormine  whethor  or  not  thoro  (^xists  a  chroniosonio  sex  dof«'nuinaii( . 
and  whether  sex  determination  may  not  bo  hrou^ht  under  Mendel's  law 
of  heredity  (sec  later  paragraphs  in  this  chapter)  in  a  modified  form. 


172 


EVOLUTION   AXD   ANIMAL   LIFE 


stimulus.  Among  ants  and  the  social  bees  and  wasps  the  males 
develop  parthenogenetically  from  unfertilized  cells,  the  fertilized 
cells  yielding  either  females  or  workers  which  are  sterile  females. 
But  this  specialized  mode  of  development  is  peculiar  to  particu- 
lar groups.  For  a  few  lower  species  it  has  been  ascertained 
that  variation  in  nutrition  may  be  a  factor  in  sex  determination. 
Favorable  nutrition  seems  to  increase  the  number  of  females. 
Most  higher  plants  are  hermaphrodite,  the  central  leaves  (car- 
pels) in  the  bud  which  becomes  the  flower,  yielding  ovules  or  fe- 


FiG.  104. — Limb  skeletons  of  various  animals,  showing  homologies  of  the  bones; 
at  left,  mole;  next,  giraffe;  next,  bat;  next,  porpoise. 


male  germ  cells.  The  next  whorl  (stamens)  yields  male  germ 
cells  or  pollen.  The  outer  whorls  (corolla,  calyx)  serve  as  pro- 
tective organs  only,  and  are  without  sex. 

The  bonds  of  union  among  organisms  which  stand  at  the 
basis  of  all  classification  are  known  as  "homologies  '^  (Figs.  101- 
104).  A  homology  is  a  real  likeness,  as  distinguished  from  one, 
merely  superficial  or  apparent.  To  superficial  likeness  we  give 
the  name  of  analogy.  Homology  means  fundamental  iden- 
tity of  structure,  as  distinguished  from  incidental  similarit}^  of 
form  or  function.  Thus,  the  arm  of  a  man  is  homologous  with 
the  foreleg  of  a  dog,  because  in  either  we  can  trace  deep-seated 
lesemblance  or  homologies  with  the  other.  In  each  detail  of 
each  bone,  nauscle,  vein,  or  rierve  of  the  one  we  can  trace  the 


HEREDITY 


173 


corresponding  details  of  the  other.  But  in  comparing  the  arm 
of  man  with  the  "hmb"  of  a  tree,  the  arm  of  a  starfish,  or  the 
foreleg  of  a  grasshopper,  we  find  no  correspondence  in  details. 
In  a  natural  classification,  or  one  founded  on  fact,  organisms 
showing  the  closest  homologies  are  placed  together.  An  arti- 
ficial classification  is  one  based  on  analogies.  Such  a  classifica- 
tion might  place  together  a  cricket,  a  frog,  and  a  kangaroo, 
because  they  all  jump,  or  a  bird,  a  bat,  and  a  butterfly,  because 
they  all  fly,  even  though 
the  wings  are  very  dif- 
ferently made  (Fig.  105) 
in  each  ca-se. 

The  very  existence 
of  such  terms  as  animals 
and  plants,  insects  and 
mollusks  imply  relation- 
ships, and  relationships 
in  different  degrees. 
Classification  is  the 
process  of  reducing  our 
knowledge  of  these 
grades  of  likeness  and 
unlikeness  to  a  system. 
By  bringing  together 
those  which  are  funda- 
mentally alike,  and 
separating  those  which 
are  unlike,  we  find  that 

these  traits  are  the  outcome  of  long-continued  influences. 
Classification  is  defined  as  "the  rational  lawful  disposition  of 
observed  facts. '^  It  rests  on  the  results  of  the  operations  of 
natural  laws,  or  forces  which  bring  about  inevitable  results. 

For  it  is  a  matter  of  common  observation  that  the  closest 
homologies  are  shown  by  those  animals  which  have  sprung  from 
a  common  stock.  The  fact  of  blood  relationship  shows  itself 
always  in  homology.  So  far  as  w^e  know,  homology  is  never 
produced  in  any  other  way,  therefore  the  actual  ])resence  of 
homologies  among  animals  or  plants  im])lies,  as  we  shall  see  in  a 
later  chapter,  their  common  descent  from  stock  possessing  these 
same  characters.  In  our  primitive  use  of  the  trunk  of  the  tree 
to  imply  unity  in  Ufe,  we  c^u  §eQ  that  this  trunk  represents 


Fig.  105. — Diagram  of  wings,  showing  homol- 
ogy and  analogy:  a,  wing  of  fly;  6,  wing  of 
bird;  c,  wing  of  bat. 


174 


EVOLUTIOX   AND   ANIMAL  LIFE 


homology,  and  that  it  is  the  representation  of  the  current  of 
heredity.     The  resemblances   arise  from   common  origin,  the 


Fig.  106. — Ears  of  various  anthropoid  apes  and  of  man,  showing  human  vestigial 
characters:  1,  hairy  human  ear;  2,  Barbary  ape;  3,  chimpanzee;  4  and  5,  human 
ears;  6,  ear  of  human  foetus;  7,  orang-outang. 


variations  from  the  demand  of  differing  external  conditions.  It 
may  be  said  that  the  inside  of  an  animal  tells  what  it  is,  the  out- 
side where  it  has  been.     In  the  internal  structure,  ancestral 

traits  are  perpetuated  with  little  change 
through  geologic  ages.  The  external 
characters  affected  by  every  feature  of 
the  surroundings  may  be  rapidly  altered 
through  response  to  demands  of  environ- 
ment and  through  the  destruction  of  in- 
dividuals whose  life  fails  of  adjustment. 

It  is  in  the  persistence  of  heredity 
that  we  find  the  explanation  of  vestigial 
organs.  An  organ  well  developed  in  one 
group  of  animals  or  plants  may  in  some 
other  be  reduced  to  an  imperfect  organ 
or  rudiment  so  incomplete  as  to  serve 
no  purpose  whatever.  Such  rudimentary 
or  functionless  structures  may  be  found 
in  the  body  of  any  of  the  higher  animals  and  in  most  or  all 
of  the  higher  plants.     As  a  rule  such  structures  are  more  fully 


Fig.  107. — Head  of  a  five- 
months  human  embryo 
showing  embryonic  hair- 
covering.     (After  Ecker.) 


HEREDITY 


175 


Fig.  108.  —  Andrian  Jeftichjew,  the 
Russian  dog  man,  showing  extraor- 
dinary covRring  of  hair  on  the  face. 
(After  Wiedersheim.) 


developed  in  the  embryo  than  in 
the  adult,  becoming  atropliied 
with  age.  Familiar  examples 
are  the  appendix  vermiformis 
and  the  unused  muscles  of  the 
ears  in  man,  the  atrophied  lung^ 
pelvis,  and  limbs  of  the  snake, 
the  air  bladder  of  the  fish,  the 
"thumb"  (or  rather  index  fin- 
ger), of  the  bird,  the  splint  bone 
of  the  horse,  and  the  like. 

The  anatomist  Wiedersheim 
has  recorded  180  vestigial  or- 
gans in  man.  These  structures 
occur  in  all  the  systems  of 
organs,  integument,  skeleton, 
muscles,  nervous  system,  sense 
organs,     digestive,     respiratory, 

circulatory,  and  urino-genital  systems.  Most  of  these  rem- 
nants of  structures  are  to  be  found  completely  developed  in 
other  vertebrate  groups.  Eleven  of  them  are  characteristic 
as  functional  organs  of  fishes  only,  four  of  ampliibians  and 
reptiles.     The  fact  that  structures  are  vestigial  is  shown  often 

by   cases   of    atavistic    de- 
velopment. 
Within 


the  brain  of 
man,  near  the  optic  lobes, 
is  a  little  spheroid  structure 
scarcely  larger  than  a  pea, 
known  as  the  ''pineal 
gland"  or  conarium.  It 
has  no  evident  function, 
and  Descartes  once  sug- 
gested that  it  miglit  be  the 
seat  of  tlie  soul.  It  is 
larger  in  the  embryo  and 
stin  larger  in  tlie  l)rains  of 
some  of  the  lower  verte- 
brates. Recent  investiga- 
tions have  shown  tliat  it 
is   especially    developed    in 


I'iG.  109. — Pineal  eye  of  lizard,  S])licuodun 
(Jluttcria).      (After  Baldwin  Sin-ncer.) 


176 


EVOLUTION  AND  ANIMAL  LIFE 


certain  lizards,  notably  in  a  very  primitive  New  Zealand  lizard 
of  the  genus  Sphenodon  (Hatteria)  (Fig.  109),  and  that,  in  these 
lizards,  the  pineal  body  ends  in  a  more  or  less  perfect  e3^e-like 
structure  placed  between  the  true  eyes  in  the  center  of  the 
forehead.  A  trace  of  this  eye  is  shown  in  the  limbless  lizard 
called  slow  worm  (Anguis),  of  Europe,  and  in  several  American 
species.     In  the  horned  toad  {Phrynosoma)  (Fig.  110)  its  place 


>5:,'-^--:r.yi.»sr- 


Fig.  110. — Head  of  lizard  or  horned  toad,  Phrynosom  hlainvillei,  showing  translucent 
pearly  skin  covering  the  pineal  eye.      (From  specimen.) 


is  covered  by  a  translucent  pearly  scale.  These  lizards  have 
in  fact  three  eyes,  and  the  pineal  body  is  the  nervous  gang- 
lion from  which  the  third  eye  arises.  The  natural  conclusion 
from  this  that  all  vertebrates  originally  had  three  eyes,  is  prob- 
ably a  too-hasty  one.  Perhaps  the  pineal  body  was  an  organ 
of  sense,  which  developed  into  an  eye  in  the  lizards  and  their 
ancestors  only,  not  in  any  of  the  Amphibians  or  fishes,  and  not 
in  any  mammals  or  birds,  although  these  are  descended  from 
reptilian  stock.  Whatever  the  origin  or  primitive  function  of 
the  pineal  ganglion,  its  existence  in  man  as  a  vestigial  organ 
is  due  to  the  persistence  of  heredity. 


HEREDITY 


177 


In  the  living  species  of  horse,  Equus,  there  is  but  a  single  toe, 
with  its  basal  bones.  On  each  side  of  tlie  base  bone  of  this  toe  is 
a  small  bone  known  as  a  si)lint  bone.  The  sj)lint  bones  are 
apparently  useless  to  the  horse,  but  in  extinct  species  of  horse 
these  bones  are  developed  as  digits,  bearing  small  hoofs.  Occa- 
sionally even  now  colts  are  born  in  which  these  splint  l)ones  bear 
rudimentary  hoofs.  In  the  museum  of  Stanford  University  is 
the  leg  of  a  high-bred  colt 
from  Milpitas,  Cahfornia,  bear- 
ing a  small  hoof  on  each  of 
the  two  splint  bones. 

The  remains  (Fig.  Ill)  of 
over  thirty  different  ancient 
horse-like  animals  have  been 
found  in  the  rocks  of  the 
Tertiary  era.  The  Eohippus, 
the  earhest  of  these  horselike 
animals,  found  in  the  oldest 
Tertiary  rocks,  was  little  larger 
than  a  fox,  and  its  forefeet 
had  four  hoofed  toes,  with  the 
rudiment  of  a  fifth,  wliile  the 
hind  feet  had  three  hoofed 
toes.  In  the  later  rocks  is 
found  the  Orohippus,  also 
small,  but  with  the  rudi- 
mentar}^  fifth  toe  of  the  fore- 
foot gone.  Still  later  appeared 
the  Mesohippus  and  Miohip- 
pus,  horses  about  the  size   of 

sheep,  with  three  hoofed  toes  only,  on  both  forefeet  and  hind 
feet,  but  with  the  rudiment  of  the  fourth  toe  in  the  forefeet, 
of  the  same  size  in  Mesohippus,  smaller  in  Miohippus.  ATso, 
the  middle  toe  and  hoof  of  the  three  toes  in  each  foot  was 
distinctly  larger  than  the  others  in  both  Mesohippus  and  Mio- 
hippus. Next  came  the  Protohippus,  a  horse  about  the  size  of 
a  donkey,  with  three  toes,  but  with  the  two  side  toes  on  each 
foot  reduced  in  size,  and  probably  no  longer  of  use  in  walking. 
The  middle  toe  and  hoof  carried  all  the  weight.  Still  later  in 
the  Tertiary  era  lived  the  Pliohippus,  an  "almost  complete 
horse/'    The  side  toes  of  Pliohippus  are  reduced  to  mere  rudi- 


FiG.  111. — Foot  changes  in  evolution  of 
the  horse:  a,  Equus,  Quaternary  (re- 
cent) ;  b,  Pliohippus,  PHocene;  c,  Pro- 
tohippus, Lower  Pliocene;  d,  Miohi]>- 
pus,  Miocene;  e,  Mesohippus,  Lower 
Miocene;  f ,Orohip pus,  Kocene.  (After 
Fig.  254  of  "Animal  Studies.") 


178 


EVOLUTION   AND   ANIMAL  LIFE 


ments  or  splints.  This  animal  differs  from  the  present  horse 
somewhat  in  skull,  shape  of  hoof,  length  of  teeth,  and  other 
minor  details.  Lastly  came  the  present  horse,  Equiis,  with  the 
splint  bones  or  concealed  rudiments  of  the  side  toes  very  small 
and  the  hoof  of  the  middle  toe  rounder.  In  spite  of  the  great 
difference  between  the  one-toed  foot  of  the  living  horse  and 
the  dog's  five-toed  foot  there  was  once  a  kind  of  horse  which 
had  a  five-toed  foot,  and  there  is  after  all  a  close  relationship 
between  the  foot  of  the  horse  and  the  foot  of  the  dog. 


Fig.  112. — Homology  of  digits  of  four  odd-toed  mammals,  showing  gradual  reduction 
in  number  and  consolidation  of  bones  above.     (After  Romanes.) 


In  man  there  is  developed  at  the  proximal  end  of  the  caecum 
or  blind  sac  of  the  large  intestine  a  small  structure  as  shown  in 
Fig.  113.  This  appendage  has  no  function,  and  it  is  subject  to 
inflammation  or  suppuration,  known  as  appendicitis.  In  the 
embryo  the  appendix  vermiformis  is  notably  larger  than  in 
the  adult  man;  and  in  the  lower  animals,  as  in  the  dog  or  the 
kangaroo  (see  Fig.  113),  it  may  be  recognizable  as  a  prolon- 
gafion  of  the  caecum,  scarcely  less  in  diameter  than  the  intestine 
itself.  The  appendix  vermiformis  is  therefore  a  vestige  of  a 
long  caecum  which  had  its  part  in  the  process  of  digestion. 

In  the  embiyo  of  all  chordate  animals,  without  exception, 
respiratory  or  gill  slits  are  developed,  homologous  with  those 
seen  in  the  embryo  of  the  fish.  The  presence  of  these  slits  or 
their  vestiges  is  one  of  the  most  important  secondary  distinctive 
characters  of  the  great  group  of  Chordata,  which  includes  the 
vertebrates.     The  human  embryo  is,  in  this  regard,  at  certain 


fil]:REDITY 


17^ 


stages  essentially  similar  to  the  embryo  of  the  fish.  But  in  the 
course  of  development  the  gill  slits  in  man  and  tlie  higher  ver- 
tebrates disappear.  Their  position  is,  however,  indicated  by 
the  course  of  certain  blood  vessels.  These  follow  the  lines 
blocked  out  in  the  embryo  when  they  led  to  the  gill  slits,  al- 
though no  other  trace  of  these  slits  persists  in  the  adult,  and  this 
direction  is  not  one  which  we  could  conceive  as  likely  to  have 
arisen  except  for  the  results  of  inheritance  from  the  lower  ver- 
tebrates. 

In  the  veins  of  the  higher  animals  valves  are  present,  so 
arranged  as  to  prevent  the  flow^  of  blood  backward  and  espe- 
cially downward  from  the  heart.  In  the  lower  animals,  tliese 
valves  are  adjusted  to  the  position  on  all  fours.  Their  adjust- 
ment is  the  same  in  man,  notwithstanding  his  erect  posture. 
Apparently  the  adjustment  of  the  valves  was  completed  before 
the  position  on  all  fours  gave  way  to  the  erect  posture. 


Fig.  113. — At  left,  appendix  vermiformis  of  kangaroo;  at  right  appendix  vermiformis 

of  human  embryo.     (After  Wiedersheim.) 


In  the  embryo  of  man  there  exists  a  regular  tail,  su})]:)orted 
by  eight  distinct  bones,  like  the  tail  of  an}^  other  mammal.  In 
the  process  of  development,  these  bones  are  reduced  in  nimiber 
and  are  joined,  forming  the  coccyx  or  rudimentary  tail. 

In  various  species  of  fishes,  lizards,  salamanders,  crayfislies, 
and  other  animals  living  in  caves  or  buried  in  the  ground,  the 
eyes  are  atrophied.  Numerous  cases  (Fig.  114)  of  tliis  sort  have 
been  studied  by  Dr.  Carl  H.  Eigenmann.  He  finds  in  general 
that  the  young  cave  fish  have  normally  developed  eyes,  but  that 


180 


EVOLUTION  AND  ANIMAL  LIFE 


with  growth  atrophy  sets  in  affecting  different  species  differ- 
ently, in  some  cases  the  muscles,  in  others  the  lenses,  but  in  all 
cases  reducing  the  size  of  the  organ  to  a  functionless  structure 
more  or  less  covered  by  the  skin.  In  all  cases,  the  ancestry  of 
these  blind  species  can  be  traced  to  forms  with  well-developed 
eyes  inhabiting  the  same  region.  Among  the  species  examined 
are  the  blind  fish  of  Mammoth  Cave  {Ainhlyopsis  spelmis),  the 
cave  bhnd  fish  of  Kentucky  and  Indiana  (Typlichthys  siibterra- 

neus) ,  descended  from 
the  Dismal  Swamp  fish 
{Chologaster  cornutus) , 
the  Missouri  blind  fish 
(Troglichthys  rosce),  the 
blind  fishes  of  the  caves 
of  Cuba  (Lucifuga  suh- 
terranea,  and  Stygicola 
dentata)  and  the  blind 
goby  of  Point  Loma 
( Typhlogohius  calif  orni- 
eiisis) . 

In  Dr.   Eigenmann's 
opinion,     the     retention 
of  eyes  in  these  species 
is   due   to   the  influence 
of    heredity,    the    vesti- 
gial structures  being 
each   and   all   necessary 
to   life  in   the   light.      Their  degeneration  he  ascribes  to  the 
inheritance  of  the  individual  effects  of  disease,  a  matter  we 
discuss  in  another  chapter. 

Hundreds  of  cases  of  vestigial  organs  in  plants  have  been 
recorded,  among  which  we  may  mention  the  barren  stamen  in 
Pentstemon  which  completes  the  number  of  five  usual  in  the 
group  of  Scrophulariacese  to  which  Pentstemon  belongs.  Other 
illustrations  are  the  rudimentary  leaves,  with  rudimentary 
stomata,  found  on  the  joints  of  species  of  cactus  (Opuntia),  etc.; 
the  cilia  found  on  the  spermatozoa  of  cycads,  which  would  en- 
able these  structures  to  move  freely  in  the  water,  although  they 
are  not  deposited  in  the  water,  and  these  cilia  are  never  actually 
used. 

By  the  theory  of  special  creation  it  was  supposed  that  these 


Fig.  114. — Fishes  showing  stages  in  loss  of  eyes 
and  color:  A,  Dismal  Swamp  fish,  Chologaster 
cornutus,  ancestor  of  the  blind  fish;  B,  Agassiz's 
cave  fish,  Chologaster  agassizi;  C,  cave  blind  fish, 
Typhlichthys  subterraneus. 


HEREDITY  181 

rudiments  were  created  in  accordance  with  the  tendency 
in  creative  processes  to  adhere  to  an  ideal  tj'pe.  But  it  can- 
not be  too  clearh^  understood  tliat  tendencies  in  biolofijy  exist 
only  as  functions  of  particular  organs.  Tlie  tendency  to 
adhere  to  a  type  is  a  part  of  heredity,  the  function  of  the  germ 
cell. 

In  the  light  of  our  knowledge  of  organic  evolution  it  is 
clear  that  the  presence  of  vestigial  organs  is  simply  a  fact  of 
heredity.  They  are  organs  once  useful,  but  which  tlirough 
changed  conditions  of  life  have  become  needless. 

It  is  a  recognized  fact  that  useless  organs  tend  to  dwindle 
away,  but  the  cause  of  this  phenomenon  is  not  so  clear.  It  may 
be  due  in  part  to  (a)  panmixia  or  cessation  of  selection,  the 
organ  being  no  longer  held  to  a  high  grade  of  efficiency,  to  (b) 
reversal  of  selection,  the  advantage  h^ing  with  those  individuals 
in  which  the  organ  is  no  longer  functional  or  (r)  the  inheritance 
of  the  results  of  functional  disuse.  The  latter  offers  an  explana- 
tion which  at  first  sight  appears  adequate,  and  its  reality  has 
been  stoutly  maintained  by  various  writers  of  the  Neo-Lamarck- 
ian  school.  In  their  views,  changes  in  the  individuals  unciues- 
tionably  due  to  individual  or  ontogenetic  disuse  are  carried  over 
to  the  species  as  phylogenetic  disuse.  Against  this  view  is 
opposed  its  inconsistence  with  current  theories  of  heredity,  and 
also  the  positive  fact  that  there  is  as  yet  no  proof  of  the  in- 
heritance of  acquired  characters. 

When  we  say  that,  through  heredity,  the  offspring  inherits 
the  characters  of  the  parent,  we  are  speaking  only  a  large  and 
general  truth.  The  details  of  this  inheritance  reveal  in  what 
regards  this  general  statement  must  be  modified.  We  have 
already  noted  the  inevitable  occurrence  of  at  least  small  varia- 
tions in  all  body  parts  in  all  individuals.  In  addition  to  this  ex- 
ception to  identical  inheritance,  certain  characters  of  the  parent 
may  not,  as  just  mentioned,  appear  at  all  in  the  offspring.  And 
this  may  be  due  to  any  one  of  several  causes. 

First,  certain  parental  characters  are  apjiarently  really  not 
heritable,  namely,  those  new  characters  which  have  been  ac- 
quired by  the  parent  during  its  lifetime  as  the  result  of  mutila- 
tion, disease,  special  use  or  disuse  of  parts,  any  change  of  parts 
due  to  direct  reaction  to  a  functional  stimulus  or  to  an  environ- 
mental stimulus  or  cause,  such  as  a  bleaching  due  to  lack 
of  light,  a  thickening  of  the  skin  in  certain  ])laces  due  to  coi' 
13 


182  EVOLUTiON  AND  ANIMAL  LIFE 

tact,  etc.  At  least,  there  is  not  recorded  any  satisfactory 
proof  of  the  inheritance  of  these  acquired  characters,  and  there 
is  definite  proof  that  many  of  them  are  not  inherited.  And 
most  biologists,  as  helpful  in  many  ways  to  a  clearing  up  of 
the  problem  of  adaptation  and  species-forming  as  the  actu- 
ality of  such  inheritance  would  be,  believe  themselves  un- 
able to  accept  this  fact,  in  the  light  of  our  present  knowl- 
edge. (This  matter  of  the  inheritance  of  acquired  characters 
is  discussed  in  Chapter  XI.  The  assumption  of  this  inheritance 
is  a  fundamental  part  of  the  Lamarckian  explanation  of  evo- 
lution.) 

Second,  certain  characters  peculiar  to  sex  are  inherited  only 
according  to  sex  and  not  by  all  the  young.  These  characters 
include  not  only  the  differing  reproductive  organs  themselves, 
but  those  many,  various,  and  often  most  remarkably  developed 
so-called  secondary  sexual  characters,  such  as  the  tufts  and 
plumes  and  brilliant  plumage  of  male  birds,  the  antlers  of  male 
deer,  the  specialized  antennae,  skeletal  processes,  and  color  pat- 
terns of  many  male  insects,  and  the  reduced  wings  of  many  female 
insects,  etc.,  etc.  Even  in  cases  of  parthenogenetic  reproduc- 
tion (i.  e.,  reproduction  in  which  the  male  takes  no  part),  sex  and 
the  sex  characters  of  the  offspring  have  no  direct  relation  to  the 
sex  and  sex  characters  of  the  mother.  The  queen  honey  bee 
produces,  in  fact,  exclusively  drones  (male  bees)  when  she  lays 
unfertilized  eggs,  while  on  the  contrary  the  parthenogenetic 
offspring  of  the  Aphids  (plant  lice)  are  all  females  for  several 
generations,  and  then  in  a  single  generation  both  males  and 
females. 

Finally,  certain  parental  characters,  even  though  blastogenic, 
may  not  appear  in  the  offspring,  but  be  inherited  by  them  in 
latent  condition,  to  appear  in  their  young  or  perhaps  even  in  a 
later  generation.  It  is  obvious,  too,  that  where  a  certain  char- 
acter in  the  mother  is  represented  in  the  father  by  one  of  oppo- 
site condition,  as  where  the  mother  is  very  short,  the  father  very 
tall,  the  mother  a  brunette,  the  father  light-haired,  a  given  child 
can  inherit  the  character  in  only  one  condition.  That  is,  in  all 
cases  of  biparental  reproduction,  and  they  compose  the  majority 
of  cases  in  both  animal  and  plant  kingdoms,  the  inherited  char- 
acters cannot  be  all  those  possessed  by  both  parents,  but  must 
be  either  those  of  one  or  the  other,  or  a  mosaic  of  them,  or  a 
blend  or  fusion  of  them.     And  this  introduces  us  to  that  phase 


herp:dity 


1S3 


of  the  stiuly  of  the  results  of  heredit}'  whicli  to-day  is  beirifi:  most 
investigated,  tlie  determination  of  the  "laws"  of  inheritance 
of  characteristics. 

The  similarity  or  dissimilarity  of  the  two  mating  parents  is  a 
matter  of  much  importance  in  regard  to  the  results  of  inherit- 
ance. To  produce  a  fertile  mating  the  two  parents  have  at 
least  to  be  nearlv  allied.     We  are  accustomed  to  take  this  for 


Fig.  115. — Romulus,  the  striped  colt  of  a  horse  mother  and  zebra  father. 

(After  Ewart.) 

granted,  but  the  actual  degree  of  phyletic  relationshi})  necessary 
in  fertile  mating  is  a  point  of  much  biologic  interest.  In  most 
cases  both  parents  must  belong  to  the  same  species  or  kiml.  l)ut 
among  animals  and  plants  there  have  been  noted  cxcei)tinns 
to  this  rule,  these  exceptions  constituting  the  facts  of  hybrith- 
zation. 

Hybridism  is  practically  limited  to  mating  of  difTerent 
species  of  the  same  genera.  Only  in  a  few  recorded  cases  liave 
organisms  of  different  genera  mated  in  nature  with  the  produc- 
tion of  oiTspring;    In  zoological  gardens  and  nienagcriQ:?  tho 


184  EVOLUTION  AND  ANIMAL  LIFE 

race  feeling  of  the  confined  animals  seems  to  break  down,  and 
unusual  cases  of  hybridism  are  occasional!}^  noted.  Also  men- 
tion must  be  made  of  the  artificial  induction  of  the  fertilization 
of  sea-urchin  eggs  by  the  sperm  cells  of  starfishes  (animals  not 
only  of  different  genera  but  of  different  classes) ,  and  a  few  other 
similar  exceptional  cases  accomplished  by  Loeb  and  other  ex- 
perimenters. In  many  examples  of  hybridism  the  immediate 
offspring  are  unable  to  produce  3'Oung  and  so  no  continuous 
series  of  generations  results.  In  other  fewer  cases  the  off- 
spring of  hybridization  are  fertile,  and  thus  constitute  the 
beginnings  of  a  new  race  or  variety  of  animal  or  plant.  Many 
of  our  domesticated  animal  races  and  cultivated  plant  varie- 
ties have  originated  by  hybridism  often  artificially  induced 
by  man. 

For  the  most  part,  however,  both  parents  of  any  brood  of 
young  belong  to  the  same  species,  and  hence  they  are  at  least  as 
like  each  other  as  the  other  members  of  the  same  species 
have  to  be.  But  this  may  still  permit  great  superficial  dissimi- 
larity: many  attributes,  such  as  size,  color,  texture,  outline, 
etc.,  of  the  body  parts,  especially  the  external  ones,  may  be 
quite  different.  For  \ythin  any  species  there  may  be  several 
subspecies  or  varieties,  the  individuals  of  all  of  which  are 
capable  of  fertile  mating  with  each  other.  And  even  where 
there  is  no  distinctly  recognizable  subspecific  distinctions  there 
may  yet  be  much  superficial  dissimilarity  among  the  individ- 
uals composing  a  single  species.  So  in  all  studies  of  the  results 
of  heredity,  of  the  actual  inheritance  of  parental  characters,  the 
degree  of  likeness  or  unlikeness  of  the  parents  must  be  taken 
into  account. 

So  that  the  "  laws  "  of  heredity,  as  formulated  on  a  study  not 
of  its  mechanism  but  of  its  results,  refer  to  the  character  of  the 
parental  union,  whether  pure  or  crossed,  and  if  crossed  whether 
the  parents  are  of  different  varieties  of  one  species  or  of  actually 
different  species.  As  a  matter  of  fact  the  crossing  of  parents 
with  a  few  to  many  dissimilar  characters  has  been  the  actual 
means  of  getting  at  some  of  the  most  important  evidence  as  to 
the  behavior  of  heredity  that  we  have.  For  the  very  dissimilar- 
ity of  the  parental  attributes  makes  it  possible  to  trace  in  the 
progeny  of  succeeding  generations  the  workings  or  results  of 
heredity  with  reference  to  these  particular  characters. 

Galton's  Law  of  Ancestral  Inheritance  may  be  stated  in  few 


HEREDITY  185 

words,  although  for  an  understanding  of  the  cliaraeter  of  the 
evidence  on  which  it  is  based, and  for  an  appreciation  of  its  wliole 
significance  some  full  account  of  it,  preferably  Gait  on 's  own 
statement  and  discussion  of  it  in  his  memoir  entitled  "The 
Average  Contribution  of  Each  Several  Ancestor  to  tlie  Total 
Heritage  of  the  Offspring,''  published  in  1897,  should  be  read. 
From  a  study  of  the  carefully  kept  i)edigree  book  of  the  kennels 
of  the  Basset  Hounds  Club,  with  records  extending  through 
twenty-two  years,  and  a  study  of  inlieritance  in  the  British 
Peerage  made  possible  by  the  comi)lete  genealogic  records 
kept  for  these  families,  together  with  a  consideration  of  va- 
rious other  less  detailed  but  at  least  helpful  records  of  inher- 
itance, Galton  formulated  the  statement  that  any  organism  of 
bisexual  parentage  derives  one  half  its  inherited  qualities  from 
its  parents  (one  fourth  from  each  parent),  one  fourth  from  its 
grandparents,  one  eighth  from  its  great-grandparents,  and  so 
on.  These  successive  fractions,  whose  numerators  are  one  and 
whose  denominators  are  the  successive  powers  of  two,  adtled 
together  equal  one  or  the  total  inheritance  of  the  organism:  thus 

Ki  +  i+TV+3V+^V+ . . . .  =1. 

The  English  mathematician  and  natural  philosopher,  Karl 
Pearson,  has  made  computations  showing  that  Galton 's  law 
thus  simply  expressed  is  only  a  close  approximation  to  the 
actual  inheritance  relations,  and  that  the  fraction  indicating  the 
contribution  of  any  given  ancestor  must  be  slightly  modified 
by  introducing  into  it  another  factor.  In  general,  though, 
the  .  Galtonian  formula  received  a  very  general  acceptance 
among  biologists.  And  only  recently,  in  the  light  of  the  discov- 
ery of  Mendel's  investigations  and  conclusions  and  their  confir- 
mation in  essential  principle  by  the  recent  researclies  of  various 
botanists  and  zoologists,  has  Galton 's  law  been  looked  on  as 
altogether  too  simple  and  incomplete  a  formulation  of  the  facts 
of  inlieritance.  It  is  not  yet  quite  certain  whether  Galton 's 
formula  is  consonant  with  the  Mendelian  formula  or  not.  But 
at  best  Galton's  law  only  expresses  a  part  of  what  may  now  witli 
confidence  be  said  to  be  known  of  the  regular  course  of  inher- 
itance. 

Before  taking  up  the  actual  Mendelian  results  and  conclu- 
sions, however,  it  is  important  for  us  to  note  the  different  modes 
or  kinds  of  behavior  of  inheritance  which  cliaracteristics  may 
show  in  their  transmission.      Cuenot   has    made  a  rough  Init 


186  i:voLutiox  and  animal  life 

suggestive  classification  of  thsse  inheritance  categories  as 
follows : 

In  cross  matings — and  by  "  cross  mating/'  students  of  hered- 
ity do  not  necessarily  mean  mating  between  distinct  species  or 
even  varieties,  but  mating  between  parents  which  disagree  in 
tlie  condition  of  one  or  more  specifically  referred  to  characteris- 
tics— in  cross  mating  betv/een  the  parents  A  and  B,  if  we  con- 
sider a  single  pair  of  corresponding  characters  a  and  h  which 
differ  in  the  two  parents,  the  young  produced  by  the  crossing 
may  (1)  all  present  the  same  parental  character  a  without  any 
trace  of  the  character  b,  the  character  a  being  then  termed 
dominant  or  prepotent  or  prevalent,  the  other  recessive  or 
latent ;  or,  (2)  the  young  may  all  agree  in  presenting  a  new  char- 
acter differing  from  the  parental  characters  a  and  h,  this  new 
character  apparently  being  a  simple  physical  mixture  or  a  real 
chemical  combination  or  blending  of  a  and  b;  or  (3),  the  young 
may  differ  from  one  another  in  regard  to  the  parental  characters 
a  and  b,  some  showing  the  character  a,  some  showing  the  char- 
acter b ;  or  (4)  the  young  may  differ  among  themselves  in  regard 
to  the  characters  a  and  b,  some  showing  the  character  a,  some 
the  character  6,  and  some  various  characters  intermediate  be- 
tween a  and  b;  or  (5)  the  young  may  show  the  characters  a  and 
b  side  by  side  in  each  individual  in  small  separated  parts,  even 
in  neighboring  but  distinct  cells.  These  differences  undoubt- 
edly depend  partly  on  the  nature  of  the  characteristics  them- 
selves, partly  on  the  kind  of  organism,  and  partly  on  extrinsic 
influences.  It  is  obvious  also  that  for  certain  characteristics  by 
no  means  all  five  of  these  ways  are  open.  Many  characters  are 
so  wholly  antagonistic  that  no  blend  nor  any  mosaic  of  them  can 
occur  in  a  single  individual,  leaving  only  ways  (1)  and  (3),  viz., 
exclusive  or  alternative  inheritance  open  to  them. 

To  these  five  general  categories  of  the  actual  transmission 
of  certain  obvious  parental  characters  may  here  be  added  for 
consideration  those  cases  of  the  appearance  in  the  young  of  o 
character  or  characters  having  no  obvious  relation  to  either  a 
or  b,  but  sometimes  explicable  as  reversions  or  reappearances 
of  characters  possessed  by  ancestors  more  or  less  remote  and 
other  times  as  obviously  w^holly  new  and  heretofore  never  ex- 
istent characters  which^  if  pronounced,  are  called  "sports"  or 
sudden  or  discontinuous  variations.  Also  must  be  taken  into 
account  the  possible  appearance  among  the  young,  of  a  few  to 


HEREDITY  187 

many  individuals  showing  man}'  simultaneous,  usualh'  sli^^ht 
but  real  differences  from  the  parents  in  various  parts  and  func- 
tions. These  are  the  differences  called  mutations  by  de  Vries 
^nd  his  followers,  and  are  the  basis  of  the  at  present  consid- 
jrrbly  accepted  theory  of  species-forming  by  heterogenesis  or 
sudden  comj^lete  fixed  modifications  of  organic  types.  In  tlie 
light  of  the  observations  and  experiments  of  de  Vries,  these  mu- 
tations are  of  special  importance  in  any  consideration  of  hered- 
ity and  variation.  (See  p.  157,  Chai)ter  IX,  for  a  brief  account 
of  these  mutations.) 

The  Mendelian  "laws"  apply  only,  probaljly,  to  certain  par- 
ticular categories  of  inheritance,  or  rather  categories  of  char- 
acters. That  is,  so  far  as  worked  out,  the  Mendelian  jjrinciples 
seem  to  have  definite  application  only  to  cases  of  inheritance  in 
which  the  characteristics  under  observation  are  nuitually  ex- 
clusive or  alternative  in  character;  categories  (1)  and  (:5)  in 
our  list  in  a  preceding  paragraph  are  the  only  ones  under  the 
rule  of  the  Mendelian  principles,  and  there  are  even  some  ex- 
ceptions in  these  categories.  The  various  other  kinds  of  inher- 
itance, called  blended  or  combined  (where  the  two  characteristics 
fuse  or  blend  to  form  a  new  condition),  and  mosaic  or  par- 
ticulate (wiiere  both  parental  characteristics  exist  side  by  side 
in  each  individual  among  the  young),  a])parently  recpiire  for 
their  explanation  something  besides  the  ]\Iendehan  principle. 

At  some  time  between  1855  and  1865  Gregor  Johann  Mendel, 
an  Augustinian  monk  in  the  small  Austrian  village  of  Briinn, 
carried  on  in  the  gardens  of  his  cloister  pedigree  cultures  of  peas 
and  some  other  plants  from  which  he  derived  data  which  he  read, 
together  with  his  interpretation  of  their  significance,  !)efore 
meetings  of  the  Natural  History  vSociety  of  Briinn,  and  wiiich 
in  the  same  year  of  their  reading  (1865)  were  published  under  the 
title  "  ExpcM'iments  in  Plant-hybridization,"  in  tlie  Ahhand- 
lungen  (vol.  iv),  of  the  society.  Mendel  was  the  son  of  a  jn^as- 
ant,  and  had  been  educated  in  Augustinian  foundations  and 
ordained  a  priest.  For  two  or  three  years  he  studied  physics 
and  natural  science  in  Vienna,  and  refers  to  himself  in  one  of  his 
papers  as  a  student  of  Kollar.  He  becanu'  abbot  of  his  cloister, 
and  was  for  a  time  president  of  tlie  Briinn  Natural  History 
Society.  Such  are  the  essential  details  of  the  education  and 
work  of  the  man  whose  name  will  undoubtedly  live  forevor  fu 
the  annals  of  biological  science. 


188  EVOLUTION   AND  ANIMAL   LIFE 

Mendel's  principal  data  were  derived  from  the  crossing  of 
varieties  of  peas  {Pisum  sativum)  in  which  he  found  several  pairs 
of  well-marked  contrasting  characters.  Bateson  gives  a  clear 
and  concise  summary  account  of  Mendel's  methods  and  results 
which  we  quote  in  the  following  paragraphs.  For  the  purposes 
of  his  experiments  Mendel  selected  seven  pairs  of  characters  as 
follows : 

1.  Shape  of  ripe  seed,  whether  round;  or  angular  and 
wrinkled. 

2.  Color  of  "endosperm"  (cotyledons),  whether  some  shade 
of  yellow;  or  a  more  or  less  intense  green. 

3.  Color  of  the  seed  skin,  whether  various  shades  of  gray  and 
gray-brown;  or  white. 

4.  Shape  of  seed  pod,  whether  simply  inflated;  or  deeply 
constricted  between  the  seeds. 

5.  Color  of  unripe  pod,  whether  a  shade  of  green;  or  a  bright 
yellow. 

6.  Nature  of  inflorescence,  whether  the  flowers  are  arranged 
along  the  axis  of  the  plant;  or  are  terminal  and  form  a  kind  of 
umbel. 

7.  Length  of  stem,  whether  about  six  or  seven  feet  long, 
or  about  three  fourths  to  one  and  one  half  feet. 

"Large  numbers  of  crosses  were  made  between  peas  differing  in 
respect  of  one  of  each  of  these  pairs  of  characters.  It  was  found  that 
in  each  case  the  offspring  of  the  cross  exhibited  the  character  of  one 
of  the  parents  in  almost  undiminished  intensity,  and  intermediates 
which  could  not  be  at  once  referred  to  one  or  other  of  the  parental 
forms  were  not  found. 

"In  the  case  of  each  pair  of  characters  there  is  thus  one  which  in 
the  first  cross  prevails  to  the  exclusion  of  the  other.  This  prevailing 
character  Mendel  calls  the  dominant  character,  the  other  being  the 
recessive  character.^ 

"That  the  existence  of  such  'dominant'  and  'recessive'  charac- 
ters is  a  frequent  phenomenon  in  cross  breeding,  is  well  knowTi  to  all 
who  have  attended  to  these  subjects. 

"  By  letting  the  cross-breds  fertilize  themselves  Mendel  next  raised 
another  generation.     In  this  generation  were  indi\dduals  which  showed 

^  ''Note  that  by  these  novel  terms  the  complications  involved  by  the 
use  of  the  expression  'prepotent'  are  avoided." 


HEREDITY  189 

the  dominant  character,  but  also  individuals  which  presented  the 
recessive  character.  Such  a  fact  also  was  known  in  a  jijood  many 
instances.  35ut  IMendel  discovered  that  in  this  generation  the  numer- 
ical proportion  of  dominants  to  recessives  is  on  an  average  of  cases 
approximately  constant,  being  in  fact  as  three  to  one.  With  very  'on- 
siderable  regularity  these  numbers  were  approached  in  the  case  of 
each  of  his  pairs  of  characters. 

"There  are  thus  in  the  first  generation  raised  from  the  cross- 
breds  seventy-five  per  cent  dominants  and  twenty-five  per  cent  re- 
cessives. 

"These  plants  were  again  self-fertihzed,  and  the  offspring  of  each 
plant  separately  sown.  It  next  appeared  that  the  offspring  of  the 
recessive  remained  pure  recessive,  and  in  subsequent  generations  never 
produced  the  dominant  again. 

"But  when  the  seeds  obtained  by  self-fertilizing  the  dominants  were 
examined  and  sown  it  was  found  that  the  dominants  were  not  all  alike, 
but  consisted  of  two  classes:  (1)  those  which  gave  rise  to  pure  dom- 
inants, and  (2)  others  which  gave  a  mixed  offspring,  composed  partly 
of  recessives,  partly  of  dominants.  Here  also  it  was  found  that  the 
average  numerical  proportions  were  constant,  those  with  pure  domi- 
nant offspring  being  to  those  with  mixed  offspring  as  one  to  two. 
Here  it  is  seen  that  the  seventy-five-per-cent  dominants  are  not  really 
of  similar  constitution,  but  consist  of  twenty-five  which  are  jnire 
dominants  and  fifty  W'hich  are  really  cross-breds,  though,  like  the 
cross-breds  raised  by  crossing  the  two  original  varieties,  they  only 
exhibit  the  dominant  character. 

"To  resume,  then,  it  was  found  that  by  self-fertilizing  the  original 
cross-breds  the  same  proportion  was  always  ai)|)roached,  namely: 
25  dominants,  50  cross-breds,  25  recessives, 
or  ID  :  2DP.  :  IR. 

"Like  the  pure  recessives,  the  pure  dominants  are  thenceforth 
pure,  and  only  give  rise  to  dominants  in  all  succeeding  generations 
studied. 

"On  the  contrary  the  fifty  cross-breds,  as  stated  above,  have 
mixed  offspring.  But  these  offspring,  again,  in  their  iiunicrical  jiro- 
portions,  follow  the  same  law,  namely,  that  there  are  three  ilominants 
to  one  recessive.  The  recessives  are  pure  like  those  of  the  last  genera- 
tion, but  the  dominants  can,  by  furtlicr  s(»lf-fertilization.  and  exam- 
ination or  cultivation  of  the  seeds  j)roduced,  be  again  shown  to  be 
made  up  of  pure  dominants  and  cross-breds  in  the  same  proportion 
of  one  dominant  to  two  cross-breds. 


190  EVOLUTION   AND  ANIMAL   LIFE 

"The  process  of  breaking  up  into  the  parent  forms  is  thus  con- 
tinued in  each  successive  generation,  the  same  numerical  law  being 
followed  so  far  as  has  yet  been  observed. 

"Mendel  made  further  experiments  wath  Pisum  sativum,  crossing 
pairs  of  varieties  which  differed  from  each  other  in  two  characters, 
and  the  results,  though  necessarily  much  more  complex,  showed  that 
the  law  exhibited  in  the  simpler  case  of  pairs  differing  in  respect  of  one 

character  operated  here  also.  _, 

"In  the  case  of  the  union  of  varieties  AB  and  ab  differing  in  -'j-vo 
distinct  pairs  of  characters,  A  and  a,  B  and  h,  of  which  A  and  B  are 
dominant,  a  and  h  recessive,  Mendel  found  that  in  the  first  cross-bred 
generation  there  was  only  one  class  of  offspring,  really  AaBb. 

"But  by  reason  of  the  dominance  of  one  character  of  each  pair 
these  first  crosses  were  hardly  if  at  all  distinguishable  from  AB. 

"By  letting  the  AaBb's  fertilize  themselves,  only  four  classes  of 
offspring  seemed  to  be  produced,  namely: 
"AB  showing  both  dominant  characters. 
''Ab  showing  dominant  A  and  recessive  b. 
"  aB  showing  recessive  a  and  dominant  B. 
"  ab  showing  both  recessive  characters  a  and  b. 
"The  numerical  ratio  in  which  these  classes  appeared  was  also 
regular  and  approached  the  ratio 

9AB  :  3Ab  :  SaB  :  lab. 
"But  on  cultivating  these  plants  and  allowing  them  to  fertilize 
themselves,  it  was  found  that  the  members  of  the 
Ratios 

1  ab  class  produce  only  ab's. 

o    j  1  aB  class  may  produce  either  all  aB's, 

(2         or  both  aB's  and  ab's. 
o     {  1  Ab  class  may  produce  either  all  ^6's 
(2         or  both  Ab's  and  ab's. 

1  AB  class  may  produce  either  aU  AB's 

2  or  both  AB's  and  Ab's, 
2  or  both  AB's  and  aB's, 
4          or  all  four  possible  classes  again, 

namely,  AB's,  Ab's,  aB's,  and  ab's, 
and  the  average  number  of  members  of  each  class  will  approach  the 
ratio  1  :  3  :  3  :  9  as  indicated  above. 

"The  details  of  these  experiments  and  of  others  like  them  made 
with  three  pairs  of  differentiat'ng  characters  are  all  set  out  in  Mendel's 


9 


memoir," 


Perhaps  the  most  striking  thing  about  ]\Icnders  work  is  tlie 
singularly  suggestive  and  luminous  interpretation  which  he  gave 
of  just  why  the  pea  characteristics  were  transmitted  exactly 
as  they  were;  why,  in  general,  the  peculiar  numerical  ratio  l^e- 
tween  dominant  and  recessive  should  be,  and  why  it  should 
persist  so  uniformly.  This  interpretation  or  explanation  is  now 
well  known  in  biology  as  the  theory  of  the  "purity  of  tlie  germ 
:ells,"  or,  as  Cuenot  has  called  it,  the  theory  of  '' gmnctes  dis- 
joints/'or  "la  disjonction  des  characteres  dans  les  gametes  des 
hybrides''  (the  separation  of  characters  in  the  germ  cell  of 
hybrids),  the  Spaltimgsgesetz  of  de  Vries. 

This  interpretation  is  simply  that  in  the  young  of  the  first 
generation  after  a  cross-mating,  although  because  of  dominance 
but  one  of  the  contrasting  pair  of  parental  characters  will  show 
itself  in  the  body  make-up,  yet  when  these  young  form  their 
germ  cells  the  two  parental  characteristics  will  be  represented, 
but  only  one  in  any  one  germ  cell;  that  is,  in  the  case  of 
Mendel's  peas  that  the  pollen  cells  and  ovule  cells  produced  by 
the  cross-bred  young  would  carry  each  one  of  the  alternative  or 
mutually  exclusive  parental  varietal  characters.  If  this  were 
the  case  and  if,  on  an  average,  the  pollen  cells  and  ovule  cells 
were  evenly  divided  as  to  the  two  characteristics,  then  by 
miscellaneous  or  random  mating  (mating  according  to  the  law 
of  probabilities)  between  these  cells  we  should  get  in  the  de- 
veloped young  just  such  conditions  with  regard  to  the  con- 
trasting characteristics  as  Mendel  actually  did  get  in  his  peas. 
For  twenty-five  per  cent  of  the  pollen  grains  representing  the 
dominant  character  would  unite  with  twenty-five  per  cent  of  the 
ovule  cells  representing  the  dominant  character,  twenty-five  per 
cent  of  the  recessive  pollen  grains  with  twenty-five  per  cent 
of  the  recessive  ovule  cells,  and  the  remaining  fifty  per  cent  of 
each  kind  with  each  other;  that  is,  of  every  four  pollen  grains  and 
every  four  egg  cells  we  should  get  by  random  })ollination  1  ])<)llen 
dominant  X  1  ovule  dominant;  1  pollen  recessive  X  1  ovule  re- 
cessive; 1  pollen  dominant  X  1  ovule  recessive;  1  ])ollen  reces- 
sive X  1  ovule  dominant.  This  condition  would  bring  it  al)()ut 
that  the  fully  developed  young  would  sliow  the  contrasting 
characteristics  (remembering  the  dominance  of  one  of  tlie  char- 
acteristics in  those  cases  in  which  dominant  and  recessive  are 
united),  in  this  condition:  31),  111.  Which  is  exactly  what 
occurred  in  Mendel's  peas,  and  has  since  been  noted  to  occur 


192  EVOLUTION  AND  ANIMAL  LIFE 

in  many  other  cases  recorded  by  post-Mendelian  observers  and 
experimenters.  These  records  are  of  both  plants  and  animals, 
and  are  fast  multiplying. 

Thus  the  so-called  Mendelian  laws  of  heredity  refer  to  two 
phases  of  the  problem  of  inheritance — viz.:  (1)  how  inherited 
characters  are  actually  distributed,  and  (2)  the  fundamental 
cause,  lying  in  the  germ  plasm,  for  this  particular  kind  of  dis- 
tribution. Like  Galton's  formula,  MendePs  law  expresses  the 
regularity  of  heredity  based  on  actual  recorded  statistics  of 
inheritance ;  but  it  also  gives  a  satisfying  fundamental  reason  for 
this  regularity.  Biologists,  with  few  exceptions,  see  in  the 
establishment  of  the  Mendelian  principles  of  heredity  in  biologic 
science  the  greatest  advance  toward  a  rational  explanation  of 
inheritance  that  has  been  made  since  the  beginning  of  the 
scientific  study  of  the  problem. 

The  extraordinary  fact  that  Mendel's  work  lay  practically 
unnoted  for  thirty-five  years  (actually  the  only  reference  to  it  in 
scientific  "  literature  "  in  all  that  time  seems  to  have  been  one  by 
Focke  in  1881  in  Die  Pfianzenmischlinge,  p.  109),  has  been 
partly  explained  by  Bateson  as  due  to  the  driving  interest  felt 
through  all  that  time  by  biologists  generally  in  other  phases  of 
investigation;  but  it  remains  a  curious  commentary  on  the 
possibilities  of  the  temporary  obscurity  that  may  be  in  store  for 
even  the  best  scientific  work.  The  "  discovery '^  of  Mendel's 
work  seems  to  have  been  made  in  1900  by  three  investigators 
almost  simultaneously,  who  also  discovered  independently  the 
same  important  facts  of  the  transmission  behavior  in  inheritance 
of  exclusive  or  alternative  characteristics.  These  men  are  de 
Vries,  Tschermak,  and  Correns,  and  their  published  papers  not 
only  verify  Mendel's  particular  work  on  the  peas,  but  confirm 
his  principles  or  laws  on  the  basis  of  much  added  experimenta- 
tion and  observation  on  other  plants.  In  the  last  five  years 
zoologists,  notably  von  Gnaita  working  with  mice,  Cuenot; 
Darbishire,  Davenport,  Bateson  and  Castle  with  mice,  rabbits, 
guinea-pigs  and  chickens,  McCracken  with  certain  beetles,  and 
Toyama,  Mrs.  Bell  and  Kellogg  with  silkworms,  have  shown 
that  Mendelian  principles  obtain  in  animal  as  well  as  in  plant 
inheritance.  For  the  results  of  all  of  these  investigations  in 
large  measure  confirm  our  confidence  in  the  IMendelian  prin- 
ciples of  dominance  and  recessivity  and  of  the  purity  of  germ 
cells.     But  also  in  nearly  all  of  these  studies  the  investigators 


HEREDITY  103 

have  found  some  inconsistencies  and  have  caught  ghmpscs  of 
other  principles  whicli,  when  finally  grasped,  will  undoul^tedly 
considerably  limit  tlie  application  of  ^Nlendel's  laws,  but  will, 
almost  certainly,  not  detract  from  their  im})ortance,  nor  lessen 
in  any  degree  the  high  place  in  science  tliat  belongs  to  the 
patient,  persistent,  clear-minded  Augustinian  monk  of  the 
cloister  gardens  of  Brimn. 

One  of  the  modifications  of  the  Mendelian  behavior  of 
hybrids  which  has  been  shown  to  exist  in  certain  cases,  is  that 
the  young  of  the  cross-mated  parents  may  not  all  exhibit  in 
the  same  degree  the  dominant  characteristic,  although  in  the 
subsequent  generations  the  regular  Mendelian  three-to-one 
splitting  up  into  dominant  and  recessive  appearance  may 
occur.  The  young  of  the  first  generation  may  include  a  very 
few  individuals  showing  the  recessive  character,  as  de  Vries  found 
in  mating  two  varieties  of  Papaver  somniferum  (ninety-seven 
per  cent  showed  the  dominant  character,  three  per  cent  the  re- 
cessive). Or  the  first  generation  may  show  a  sort  of  pseudo- 
blend  condition,  approaching  but  not  duplicating  exactly  the 
dominant  characteristic,  as  occurs  when  Hyoscyamus  pallidas 
is  crossed  with  H.  niger  (de  Vries,  ''Die  Mutationstheorie," 
Bd.  II.,  p.  162.) 

When  silkworm  moths  of  the  race  Shanghai,  with  white 
cocoons,  are  crossed  wdth  moths  of  the  race  Yellow  Var.  with 
rose-yellow  cocoons,  the  hybrid  offspring  make  straw-yellow 
cocoons  of  a  tint  just  between  the  two  parent  tints.  The  color- 
ing matter  of  the  grapevine  Aramon  has  the  chemical  formula 
C46H36O20J  and  the  coloring  matter  of  the  race  Teinturier  has 
the  formula  C44H40O20*  the  hybrid  offspring  called  Pctit- 
Bouschet,  of  a  crossing  of  these  two,  has  coloring  matter  of  the 
formula  C45H3g02o,  exactly  intermediate.  These  are  specific 
cases  of  blended  inheritance  and  there  are  many  others  known. 
Mendel  once  got  as  the  result  of  a  crossing  between  two  pva 
races,  one  one  foot  in  height  and  the  other  six  feet,  hyl)nds 
measuring  from  six  to  seven  and  one  half  feet  high. 

Also  when  the  plant  Mirabilis  jalapa  ?  ,  with  red  flowei-s, 
is  crossed  with  a  male  variety  with  white  flowers  the  hybrid 
offspring  exhibit  red  flowTrs  (maternal  typo),  white  flowers 
(paternal  type),  and  flowers  streaked  with  the  two  colors.  So 
when  corn  with  blue  kernels  is  crossed  with  corn  with  white 
kernels,  a  hybrid  is  obtained  exhibiting  on  a  single  ear  blue 


194 


EVOLUTION   AND   ANIMAL   LIFE 


kernels^  white  kernels,  kernels  of  intermediate  bluish-white  tint 
and  kernels  streaked  with  blue  and  white.  The  streaked  flowers 
and  kernels  of  these  two  cases  are  due  to  mosaic  inheritance. 

Or  the  apparent 
dominance  of  the 
contrasting  charac- 
teristics may  be 
proved  to  have 
something  of  real 
dominance  about  it, 
as  Miss  McCracken 
has  so  clearly  shown 
in  her  studies  of 
the  inheritance  of 
dichromatism  in  the 
little  beetles  Lina 
lapponica  (Fig.  117) 
and  Gastroidea  dis- 
similis.  Here  the 
first  two  or  three 
generations  behave 
in  true  Mendelian 
manner,  but  with 
successive  generations  the  dominant  character  is  })lainly  seen  to 
be  gradually  extinguishing  the  recessive  character  in  the  cross- 
bred groups,  so  that  in  the  seventh  generation  after  the  originri 
cross-mating  the  Mende- 
lian ratio  of  2  to  1  in 
the  cross-bred  group  is 
changed  to  28  to  1. 

There  may  occur  also 
a  breaking  up  or  decom- 
position of  the  parental 
varietal  characters,  which 
may  mean  that  the  domi- 
nant and  recessive  char- 
acters are  not  simple 
ones  but  are  complex — ■ 

i.  e.,  realh'  the  resultant  of  several  combined  characteristics;  or 
it  may  mean  that  there  exists  a  real  instability  in  the  parent 
type  and  that  the  stimulus  or  influence  of  the  cross-mating  is  all 


Fig.  116. — At  left  an  ear  of  fiel  1  corn;  at  right  an  ear  of 
sweet  corn;  and  in  the  middle  a  hj'bricl  of  these  two, 
showing  alternation  of  kernels  resembling  those  of 
each  different  parent.     (After  de  Vries.) 


Fig.  117. — Lina  lapponica,  showing  its  two  forms, 
one  black  and  one  spotted.    (After  McCracken.) 


HEREDITY  195 

that  is  needed  to  break  down  this  weak  apparent  stabihty  of  il:(> 
type  and  allow  its  component  characters  (the  elementary  units 
of  de  varies)  to  recombine  into  various  new  and  differing  types. 
This  condition  seems  to  be  that  which  results  in  tlie  extraordi- 
nary variation  so  commonly  observed  by  plant  and  animal 
breeders  as  brought  out  by  hybridization,  and  which  is  con- 
stantly made  use  of  by  these  breeders.  Luther  Burlmnk  tlc- 
pends  very  largely  on  this  initial  abundant  and  eccentric  varia- 
tion induced  by  wide  hybridizations  for  "starters  "  for  his  work 
of  producing  "new  creations/' 

So  in  accepting  Mendel's  laws  of  heredity  we  must  Vjear 
clearly  in  mind  that  the}'  by  no  means  apply  to  all,  or,  at  any 
rate,  that  our  present  knowledge  of  them  does  not  include  tlicir 
application  to  all,  cases  and  categories  of  inheritance. 


CHAPTER  XI 
INHERITANCE    OF  ACQUIRED  CHARACTERS 

Tout  ce  qui  a  ete  acquis,  trace  ou  change  dans  Torganisation  des 
individus,  pendant  le  cours  de  leur  vie,  est  conserve  par  la  generation 
et  transmis  aux  nouveaux  individus  qui  proviennent  de  ceux  qui  ont 
eprouve  ces  changements. — Lamarck. 

Heaven  forfend  me  from  Lamarck  nonsense  of  a  tendency  to  pro- 
gression, adaptation  from  the  slow  willing  of  animals,  etc. ;  but  the 
conclusions  I  am  led  to  are  not  wholly  different  from  his,  though  the 
means  of  change  are  wholly  so. — DAmviN  to  Hooker,  1848. 

The  "fourth  Law  of  Evolution,"  as  expressed  by  Lamarck 
in  his  "Zoological  Philosophy,"  reads  as  follow^s:  "All  that  has 
been  acquired,  begun,  or  changed  in  the  structure  of  individuals 
in  their  lifetime,  is  preserved  in  reproduction  and  transmitted  to 
the  new  individuals  which  spring  from  those  which  have  in- 
herited the  change." 

This  principle  was  used  by  Lamarck  as  one  of  the  funda- 
mental elements  in  his  theory  of  the  transmutation  of  species. 
For  nearly  a  hundred  years  it  attracted  little  attention,  being 
accepted  as  a  part  of  the  law  of  heredity  by  most  persons,  even 
by  those  most  opposed  to  the  essential  part  of  Lamarck's  theory, 
the  derivation  or  transmutation  of  species.  Among  others, 
Darwdn  accepted  it  as  one  of  the  factors  in  evolution  of  forms. 
With  Herbert  Spencer  it  became  one  of  the  fundamental  prin- 
ciples of  the  philosophy  of  Evolution.  Mr.  Spencer  states  tlie 
proposition  in  this  way:  "Change  of  function  produces  change 
of  structure:  it  is  a  tenable  hypothesis  that  changes  of  structure 
so  produced  are  inherited."  For  the  supposed  inheritance  of 
characters  produced  by  the  impact  of  environment  or  by 
resultant  activities  of  the  individual  the  term  progressive 
heredity  has  been  devised.     The  fact  of  the  existence  of  pro- 

196 


INHERIT AN'OE   OF  ACQUIRED  CIL-UIACTERS  107 

gressive  heredity,  more  or  less  taken  for  granted  by  writers  of 
the  last  centmy,  was  flatly  denied  by  Dr.  August  Weismann, 
w^ho  insisted  that  it  was  necessary  that  the  theory  of  the 
inheritance  of  characters  acquired  in  tlie  hfetime  of  tlie  indi- 
vidual should  no  longer  be  accepted  without  definite  j^roof. 

In  the  theory  of  heredity  through  the  devc'l()])nient  of  the 
germ  cell  controlled  by  influences  exerted  by  structures  within 
the  nucleus,  Weismann  found  no  room  for  the  inheritance  of 
characters  not  preestablished  within  this  germ.  External  in- 
fluences in  general  cannot  reach  the  germ  cells,  and  throughout 
nature  the  germ  cells  are  elaborately  i)rotocted  from  tlie  direct 
influence  of  external  conditions. 

This  attack  upon  an  ancient  theory  rousc.'d  its  supporters 
to  defend  their  fr.ith  and  to  search  foi-  evidence  to  support  it. 
A  temporary  division  of  naturalists  into  two  scliools  arose  as  a 
result  of  this  discussion.  Those  wlio  l:eld  with  Lamarck  and 
Spencer  that  characters  gained  in  tlie  life  time  of  the  individual, 
and  not  received  from  ancestors  possessing  them,  l)ecame  hered- 
itary, were  known  as  Neo-Lamai'ckians.  Those  who,  with 
Weismann,  denied  the  existence  of  this  factor  and  from  a  neces- 
sity, real  or  fancied,  laid  special  stress  on  the  Darwinian  principle 
of  natural  selection,  assumed  the  title  of  Neo-Darwinians.  In 
their  hands  the  Darwinian  principle  became  the  all-})owerful 
factor  in  evolution,  a  theory  of  Albnacht  which  was  soon 
questioned  from  other  quarters  and  bv  those  not  considered  as 
^  Neo-Tamarckians.  Prominent  among  the  leaders  of  the  Xeo- 
Lamarckians  were  Herbert  Spencer,  Haeckel,  Nageli,  Cope, 
Eimer,  Hyatt,  Gadow,  Dall,  Packard,  and  others.  Among 
the  recognized  Neo-Darwinia,ns  were' Weismann,  Wallace,  Hux- 
ley, Gray,  Brooks,  liankester,  and  others. 

After  some  vears  of  controversv,  mostly  theoretical,  the  dis- 
cussion  has  been  tacitly  dropped  by  biologists  generally.  It  is 
recognized  that  the  sole  crucial  test  is  that  of  experiment,  tliat 
experiment  is  not  easy,  inasmuch  as  it  is  v(M'y  difficult  to  show 
that  any  given  trait  in  lieredity  really  belongs  to  the  category 
of  acquired  characters,  and  that  in  no  case  has  it  l-)een  indu- 
bitably sliown  that  any  charactei  not  inborn  has  been  inherited. 
Moreover  the  studies  of  the  germ  cell  and  the  j^liysical  basis  of 
heredity  tend  to  show  that  the  structures  of  the  germ  cell  are 
more  complex  and  that  the  processes  of  heredity  are  in  a  sense 
more  mechanical  than  could  have  been  supposed  in  the  time  of 
14 


lOS  EVOLUTION  AND  ANIMAL  LIFE 

Lamarck  or  even  that  of  Darwin  cr  Spencer.  The  characters 
shown  by  any  adult  individual  are  all  in  a  sense  acquired  char- 
acters, their  development  dependent  largely  on  nutrition  and  on 
the  influences  of  environment.  The  facts  of  heredity  show  that 
it  is  not  the  actual  traits  of  the  parents,  but  rather  their  poten- 
tialities which  are  inherited.  Moreover,  acquired  characters 
are  simply  matters  of  degree  of  development.  They  represent 
in  no  case  anything  qualitatively  new.  Taking  the  modern 
theories  of  heredity,  it  is  perhaps  not  conceivable  that  "all  that 
is  acquired,  begun,  or  changed"  in  the  physical  or  mental  life 
of  the  individual  should  jjroduce  a  corresponding  change  in  the 
germ  cells,  or  in  the  cells  from  which  these  are  thrown  off. 

On  the  other  hand.  Dr.  Weismann  has  admitted  the  possi- 
bility that  one-celled  animals  and  animals  of  simple  structure 
in  which  the  germ  cell  shares  in  the  general  relation  of  the  body 
cells  to  the  environment  may  be  effected  by  developmental  con- 
ditions. In  other  w^ords,  the  inheritance  of  acquired  characters 
may  be  a  reality  in  the  development  of  Protozoa,  the  simpler 
Metazoa,  and  the  lower  types  of  plants,  but  this  condition  does 
not  obtain  among  the  higher  forms. 

In  much  of  the  discussion  on  this  subject  the  term  "ac- 
quired characters ''  is  used  with  an  uncertain  or  double  meaning. 
The  term  should  be  limited  to  traits  of  the  individual  which 
were  not  inborn  or  blastogenic,  and  would  not  be  exhibited  in 
the  natural  or  usual  development  of  the  individual.  In  general, 
such  traits  would  arise  either  from  the  operation  of  use  or  disuse 
of  parts,  or  other  functional  stimulation  derived  from  the  en- 
vironment. 

An  illustration  of  an  acquired  character  resulting  from  use 
and  disuse  would  be  the  increased  size  of  the  arm  in  the  black- 
smith, or  tlie  decreased  leg  muscles  of  the  tailor.  The  training 
of  a  musician  or  of  a  mathematician  would  give  increased  power 
along  the  hues  of  the  training.  The  neglect  of  the  musical  or  of 
mathematical  ability  would  lead  to  the  relative  mediocrity  of 
this  form  of  ability.  Education  in  a  general  way  increases  mental 
capacity:  neglect  of  education  allows  it  to  become  relatively 
less.  The  supposed  inheritance  of  results  of  civilization  forms 
an  important  part  of  the  philosophy  of  Herbert  Spencer.  Is 
civilization  the  inheritance  of  the  power  gained  by  past  suc- 
cesses, or  is  it  simply  the  acquisition  of  the  machinery  which 
past  successes  have  produced?     As  to  this  Herbert  Spencer 


INHERIT A.\CE   OF   ACQUIPTD  CHARACTERS  100 

remarks:  " Considerinf!;  tlic  width  did  d{'j)tli  of  tlie  cfTocts 
which  the  acceptance  of  one  or  the  oth(>r  of  these  liypotlieses 
must  have  on  our  views  of  hfe,  the  question,  Wliich  of  them  is 
tfue?  demands  beyond  all  other  ({uestions  whatever  the  atten- 
tion of  scientific  men." 

Other  illustrations  of  the  supposed  effect  of  use  and  disuse 
are  thuG  discussed  by  Dr.  Edwin  Grant  Conklin: 

"In  the  first  place,  this  whole  line  of  arj2;umont  starts  with  the 
assumption  that  the  individual  habits  of  an  animal  arc  iiilicritcd,  and 
that  these  habits  ultimately  determine  the  structure,  an  assumption 
which  really  begs  the  whole  question;  for,  after  all,  tho  substratum  of 
any  habit  must  be  some  physical  structure,  and  if  modifio<i  haljits  are 
inherited  it  must  be  because  some  modified  structure  is  inherited.  I 
take  an  example  which  will  serve  as  an  illustration  of  a  whole  class: 
Jackson  says  that  the  elongated  siphon  of  Mya,  the  long-necked  clam, 
is  due  to  its  habit  of  burrowing  in  the  nmd,  or  to  ({uote  his  words: 
'It  seems  very  evident  that  the  long  siphon  of  this  genus  was  brought 
about  by  the  effort  to  reach  the  surface,  induced  by  the  habit  of  deej) 
burial.'  It  certainly  would  be  pertinent  to  in([uire  where  it  got  this 
habit,  and  how  it  happened  to  be  transmitted.  It  is  surely  as  diffi- 
cult to  explain  the  acquisition  and  inheritance  of  habits,  the  basis  of 
which  we  do  not  know,  as  it  is  to  explain  the  acquisition  and  inlieri- 
tance  of  structures  which  are  tangible  and  visible.  Such  a  method 
of  procedure,  in  addition  to  begging  the  whole  question,  commits  the 
further  sin  of  reasoning  from  the  relatively  unknown  to  the  relatively 
known. 

"This  case  is  but  a  fair  sample  of  a  whole  class,  among  wliich  may 
be  mentioned  the  following:  The  derivation  of  the  long  hind  legs  of 
jumping  animals,  the  long  forelegs  of  climbing  animals,  and  the  elon- 
gation of  all  the  legs  of  rumiing  animals  through  the  influence  of  an 
inherited  habit.  All  such  cases  are  open  to  the  very  serious  objection 
mentioned  above. 

''Another  whole  class  of  arguments  may  be  reduced  to  this  propo- 
sition: Because  necessary  mechanical  conditions  are  never  violated 
by  organisms,  therefore  modifications  due  to  such  conditions  show 
the  inheritance  of  acquired  characters.  Plainly,  the  alternative  j)ropo^ 
sition  is  this:  if  acquired  characters  t^re  not  inhonted,  organisms  ought 
to  do  impossible  things. 

''Many  of  the  arguments  advanced  to  prove  the  inheritance  of 
pbf^rftGt^rs  aoqiurt?4  throvigh  ^se  or  Jiguse  seem  to  me  to  prove  ep^i^iy 


200  EVOLUTION   AND  ANIMAL   LIFE 

too  much.  For  example,  Professor  Cope  argues  very  ably  that  bones 
are  lengthened  by  both  stretch  and  impact,  and  that  modifications 
thus  produced  are  inherited.  Even  gi'anting  that  this  is  true,  how 
would  it  be  possible  for  this  process  of  lengthening  to  cease,  since 'in 
active  animals  the  stretch  and  impact  must  be  continual?  Professor 
CojDe  answers  that  the  growth  ceases  when  '  eciuilibrium '  is  reached. 
I  confess  that  I  cannot  miderstand  tliis  explanation,  since  the  assumed 
stimulus  to  growth  must  be  continual.  But,  granting  again  that 
growth  may  stop  when  an  animal's  legs  become  long  enough  to  'sat- 
isfy its  needs,'  how  on  this  principle  are  we  to  account  for  the  shorten- 
ing of  legs,  as,  for  example,  in  the  turnspit  dog  and  the  ancon  sheep 
and  numberless  cases  occurring  in  nature?  If  any  one  species  was 
able,  by  taking  thought  of  mechanical  stresses  and  strains,  to  add  one 
cubit  mito  its  stature,  how  could  the  same  stresses  and  strains  be 
invoked  to  decrease  its  stature? 

"These  e\adences  are,  I  know,  not  the  strongest  ones  which  can  be 
adduced  in  support  of  the  Lamarckian  factors.  There  are  at  present 
a  relatively  small  number  of  such  arguments  which  seem  to  be  valid 
and  the  great  force  of  vrhich  I  fully  admit.  But  the  cases  which  I  have 
cited  are,  I  believe,  fair  samples  of  the  majority  of  the  evidences  so 
far  presented,  and  in  the  face  of  such  'evidence'  it  is  not  surprising 
that  one  who  is  himself  a  profound  student  of  the  subject  and  a  con- 
Ainced  Lamarckian  prays  that  the  Lamarckian  theory  may  be  dehv- 
ered  from  its  friends.''  ^ 

As  to  the  inheritance  of  the  effects  of  extrinsic  forces  on 
the  indi\'idual,  we  find  little  in  the  way  of  direct  evidence. 

In  all  the  members  of  the  large  family  of  fiomiders  and  soles, 
the  adult  fish  rests  flat  on  the  bottom  and  swims  on  its  side,  the 
cranium  being  tAvisted  so  that  both  eyes  appear  on  the  upper 
side.  As  a  rule  color  cells  are  developed  on  the  upper  side  only, 
the  lower  cells  remaining  largely  uncolored  or  white.  In  the 
young  of  all  species  the  head  is  symmetrical,  both  eyes  being 
normally  situated,  and  the  fish  swims  vertically  in  the  w^ater. 
Little  by  little,  as  development  goes  on,  the  fish  turns  over  to 
one  side,  and  the  eye  of  the  lower  side  passes  around  or  through 
the  forehead  to  join  its  fellow  on  the  upper  side.  On  the  upper 
side  pigment  cells  develop,  w^hile  on  the  low^er  side  they  remain 

^H.  F.  Osbom,  ''Evolution  and  Heredity,"  Wood's  HoU  Biological 
j^eutures,  1890. 


Inheritance  of  acquired  characti^rs        201 

imperfect.  However,  in  a  flounder  reared  under  conditions  in 
which  the  hght  falls  on  the  lower  side,  pigment  cells  are  de- 
veloped also  on  til  at  side. 

It  has  been  claimed  by  certain  writers,  as  Cunningham,  that 
the  twisting  of  the  head  in  the  flounder  is  due  to  tlie  inheritance 
of  an  acquired  character.  A  flat  fish  without  air  bladder,  rest- 
ing on  the  sea  bottom,  naturally  falls  on  one  side.  The  eye 
thrust  into  the  sand  is  naturally  twisted  around  to  the  upper 
side,  and  +his  tendency  begun  in  very  young  individuals  becomes 
hereditary,  while  the  lack  of  pigment  on  the  under  side  is  also 
transmitted  by  inheritance.  But  it  is  just  as  easy  lo  claim 
that  the  first  trait  of  adaptation  is  due  to  natural  selection,  and 
that  the  whiteness  of  the  blind  side  is  ontogenetic,  due  to  the 
absence  of  light  in  the  growth  of  the  individual.  In  any  case,  no 
specific  theory  of  the  origin  of  the  twist  of  the  floimder's  head 
can  be  regarded  as  proved. 

It  is  well  known,  as  Dr.  Conklin  observes,  that  certain  water 
snails  "if  reared  in  small  vessels  are  smaller  than  when  grown 
in  large  ones,''  and  this  case  has  been  cited  as  sliowing  the 
influence  of  environment  in  modifying  species.  Th.ere  is  good 
evidence,  however,  that  this  modification  does  not  affect  the 
germinal  protoplasm,  for  these  same  gasteropods  will  grow 
larger  if  placed  in  larger  vessels.  It  seems  very  piobable  that 
the  diminished  size  of  these  animals  is  due  to  deficient  food 
supply,  but  this  has  so  little  modified  the  somatic  protoi)lasm 
that,  although  the}^  may  be  fully  developed  as  shown  by  sexual 
maturity,  they  at  once  increase  in  size  as  soon  as  more  abundant 
food  is  provided,  and  this  takes  place  by  the  active  growth  and 
division  of  all  the  cells  of  the  body.  In  higher  animals,  once 
maturity  has  been  reached,  there  is  little  chiwice  for  growth, 
apparently  because  many  of  the  cells  are  so  highly  dilTeren- 
tiated  that  they  can  no  longer  divide;  consequently  the  giowth 
is  limited,  and  hence  the  size  of  the  adult  may  depend  in  part 
upon  the  amount  of  nutriment  furnished  to  the  embryo.  This 
limitation  of  growth  is  due  to  the  high  degree  of  tlilTerentiation 
of  the  somatic  cells.  But  as  the  geiin  cells  are  not  highly  dif- 
ferentiated and  are  capable  of  division,  it  follows  that  they 
would  not  be  permanently  modified  by  starving.  It  may  be. 
as  Professor  Brewer  argues,  that  long-continued  starving  and 
consequent  dwarfing  of  animals  may  leave  its  mark  on  the 
germinal  plasm;  but,  as  he  also  remarks,  this  influence  nuist  be 


202  EVOLUTION  AND  AKIMAL  LIFE 

very  slight  as  compared  wxch  the  cumulative  effects  of  selection 
in  breeding,  and  it  is  safe  to  assert  that  there  is  no  such  whole- 
sale and  immediate  modification  of  the  germinal  plasm  due  to 
nutrition  as  some  people  seem  to  suppose/' 

As  a  matter  of  fact  experiment  has  showm  that  the  results  of 
dwarfing  due  to  lack  of  food  are  shown  for  three  generations  in 
silkworms  (these  subsequent  broods  of  larvae  being  full  fed 
but  producing  dwarfed  moths).  But  with  succeeding  genera- 
tions the  moths  became  larger  and  resumed  their  normal  ap- 
pearance. 

Mutilations  of  any  sort  are  not  inherited.  The  tails  of 
sheep  have  been  cut  off'  for  countless  generations.  Yet  each 
lamb  is  born  with  a  tail.  This  law  holds  good  for  docked  tails, 
docked  ears,  pierced  ears,  and  the  many  mutilations  to  w^hich 
domestic  animals  and  men  have  been  subject  since  the  begin- 
ning of  civilization. 

Influences  of  climate,  of  heat,  of  cold  are  not  inherited  so 
far  as  experiment  shows,  nor  has  it  been  made  clear  that  any 
extrinsic  influence  exerted  on  the  individual  reallv  modifies 
the  forces  of  heredity.  Even  Lamarck  admits  this.  He  ob- 
serves: "Circumstances  change  the  forms  of  animals.  But  I 
must  not  be  taken  literally,  for  environment  can  effect  no  direct 
changes  whatever  upon  the  organization  of  animals. '^ 

In  Spencer's  view,  the  phenomena  of  instinct  are  to  be  ex- 
plained as  the  inheritance  of  habits  of  the  individual.  The 
Neo-Darwinians  see  in  the  adaptations  of  instinct  only  the  re- 
sults of  natural  selection  acting  upon  the  endless  variations  to 
w^iich  individual  instincts  are  subject.  In  most  cases  the  latter 
view  seems  the  most  probable.  In  some  cases  it  hardly  offers 
a  plausible  expk-nation. 

The  young  mocking  bird  shows  an  inborn  dread  of  owls  and 
cats,  while  it  is  relatively  indifferent  to  the  presence  of  dogs  or 
chickens.  It  seems  hardly  reasonable  to  suppose  that  all 
mocking  birds  without  this  instinct  of  dread  for  these  ptrticular 
animals  have  been  destroyed,  while  the  others  have  survived. 
Still  more  deep  seated  is  the  dread  of  snakes  possessed  by  all  the 
monkey  species  known  to  us,  as  well  as  by  their  human  allies. 
Most  men  and  most  monkeys  have  a  different  feeling  in  regard 
to  snakes  from  that  exhibited  toward  any  other  sort  of  animals. 
This  feeling  is  inborn.  It  may  be  suppressed,  but  not  often 
wholly  conquered.     To  call  it  an  inherited  experience  is  easy, 


INHERITANCE   OF   ACQUIRED  CIIARACTERb  203 

but  in  (Jcfiiult  of  other  ideiu'c  for  tlio  inhoritjincc  of  experi- 
ences, the  exj)hinati()n  is  not  satisfactory.  But  it  is  not  easy 
to  bcHcve  that  in  early  times  those  witliout  this  instinct  fell 
victims  to  venomous  snakes  througii  tlieir  own  fearlessness.  It 
is  perhaps  not  necessary  to  take  sides  on  this  question.  Any 
view  we  may  adopt  rests  for  confirmation  mainly  on  the  im- 
probability of  what  we  conceive  to  be  the  opposite  alternative. 
Conklin  further  observes  that  the 

"so-called  facts  [of  progressive  heredity]  are  merely  probabilities  of  a 
higher  or  lower  order,  and  to  one  man  they  seem  more  important  than 
to  another.  No  conviction  based  even  upon  a  high  degree  of  proba- 
bility can  ever  be  reached  in  tliis  way.  There  is  here  a  deadlock  of 
opinion,  each  challenging  the  other  to  produce  indubitable  ]>r<)()f. 
This  can  never  be  furnished  by  observation  alone.  Possibly  even 
experiment  may  fail  in  it,  but  at  least  it  is  the  only  hope." 

We  shall  not  assist  science,  says  Osl^orn, 

"wdth  any  evolution  factor  grounded  uj)on  logic  rather  than  upon 
inductive  demonstration.  A  retrograde  chapter  in  the  history  of  sci- 
ence would  open  if  we  do  so  and  should  accept  as  established  laws 
those  which  rest  so  largely  upon  negative  reasoning." 

Meanwhile  we  may  regard  the  theory  of  the  inheritance  of 
acquired  characters  as  a  piece  of  useful  scaffolding  which  has 
served  its  punpose  in  the  development  of  the  facts  of  the  deriva- 
tion of  species.  At  present  most  of  it — perhaps  all  of  it — must 
be  taken  down,  but  it  may  be  that  from  the  same  base  will  arise 
a  better  constructed  theory  which  will  again  serve  a  ])urpose 
in  the  study  of  organic  evolution. 

Similar  conditions  in  life  tend  to  develop  or  encourage 
analogous  adaptations  in  groups  of  animals  not  homologous  in 
structure  nor  closely  related  by  lines  of  descent.  In  many  cases 
these  adaptations  are  so  very  similar  and  are  so  subtle  in  their 
parallelism  as  to  deceive  even  the  trained  naturalist.  In  other 
cases,  the  convergence  and  its  consetpient  analogies  are  less 
perfect,  and  the  separate  influence  of  like  selection  und(M-  like 
environment  is  easily  traceable. 

Examples  of  this  sort  are  seen  in  the  density  of  the  fur  of  all 
Arctic  animals,  whatever  the  group  to  which  they  belong.  An- 
other illustration  is  found  in  tbc  whit^^  winter  dress  of  wcuseb, 


204  EVOLUTION   AND   ANIMAL   LIFE 

rabbits,  owls,  ptarmigans,  and  other  birds  and  mammals,  this 
color  aiding  aHke  in  defense  or  attack  as  against  the  back- 
ground of  snow.  Similar  convergence  of  characters  is  seen  in 
the  gray  hues  of  almost  all  desert  animals,  in  the  thorny  stems 
and  scant  thick  foliage  of  almost  all  desert  plants.  In  swift 
streams,  fishes  of  various  types  (sculpins,  darters,  gobies,  cat- 
fish, and  minnows)  protect  themselves  from  the  current  by  the 
reduction  of  the  air  bladder,  by  the  instinct  to  lie  flat  on  the 
bottom,  and  the  instinct  to  make  short  c|uick  darts  from  place  to 
place  in  the  swift  waters.  To  this  end  also,  certain  fuis  are  in 
each  case  especially  increased  in  size  and  force. 

Convergence  of  characters  is  shown  in  the  black  colors,  soft 
bodies,  and  luminous  spots,  characteristic  of  different  groups  of 
deep-sea  fishes.  It  also  appears  in  the  development  of  eellike 
forms  in  groups  of  fishes  whicli.  have  no  affinity  with  eels,  and 
of  snakelike  forms  among  .lizards  and  salamanders,  which  have 
no  real  affinity  with  snakes.  Like  conditions  of  life  bring  about 
like  structures.  We  may  instance  the  occurrence  of  blind  fishes 
of  various  groups  in  the  different  cave  areas,  these  species  being 
derived  in  all  cases  from  fishes  of  neighboring  regions  having 
well-developed  eyes.  Thus  the  blind  cave  fish  of  Missouri  {Trog- 
lichthys  rosce),  and  those  of  Indiana  and  Kentucky  (Avihlyopsis 
spelceus,  Typhlichthys  suhterraneus) ,  are  separately  derived  from 
the  once  widespread  t3^pe  of  the  Dismal  Swamp  fish  {Cholo- 
gaster  cornutus) .  The  blind  fishes  of  Cuba  (Stygicola,  Lucifuga) 
are  derived  from  ancestors  of  a  marine  cusk  (Brotula)  now  found 
in  the  Cuban  seas.  The  blind  catfish  of  Pennsylvania  (Gronias 
nigrilabris)  is  modified  from  an  existing  species  {Ameiurus 
pullus)  found  in  the  same  region.  The  blind  salamanders  of 
Austria  and  Texas  are  derived  from  former  inhabitants  of  the 
same  regions  which  possessed  well-developed  eyes. 

Parallelisms  of  this  sort  are  found  in  every  group  of  animals 
and  plants.  It  is  generally  easy  to  distinguish  analogous 
variations  or  results  of  convergence  of  characters,  by  the  study 
of  comparative  anatomy.  Resemblances  induced  by  like  selec- 
tion or  by  like  conditions  are  usually  superficial  and  do  not 
affect  those  structures  which  do  not  come  into  direct  contact 
with  external  conditions.  But  sometimes  even  deep-seated 
characters  have  been  reached  and  affected  by  environmental 
influences.  In  this  case  a  finer  test  is  found  in  the  study  of 
embryonic  development.     In  general,  creatures  actually  closely 


IXMERITAXCE   OF   ACXJI'lRi:!)  CHARArTKRS  205 

related  in  descent  have  inherited  common  methods  of  develop- 
ment. Thus  to  embryology  we  have  looked  for  the  final  test 
as  to  the  real  aflinities  of  any  given  form.  lUit  even  this  test  is 
sometimes  delusive,  for  selection  and  environmental  influences 
may  affect  embryonic  development,  as  tliey  may  affect  every 
other  character  or  instinct. 

Certain  writers  carry  this  thought  further,  and  find  no  real 
basis  for  discrimination  l)etween  homologies  und  analogies. 
They  would  hold  that  the  ])rogressivc  inlieritance  of  effects  of 
similar  environment  miglit  in  time  i)r()duce  forms  not  innne- 
diately  related  into  a  condition  of  practical  identity  each  with 
the  other. 

Professor  Hans  Gadow  observes: 

"When  Gegeiibaur  had  become  the  founder  of  modern  comjiarative 
anatomy  by  putting  it  on  the  basis  of  evolution,  it  Ijccanio  gradually 
an  axiom  that  homologies  determined  the  degrees  of  affinity,  and  now 
in  turn  the  position  of  an  animal  in  the  system  is  ai)pcal('d  to  for  de- 
termining whether  a  given  organ  is  homologous  or  only  analogous. 
It  is  a  vicious  circle.  'Only  analogous'  is  the  usual  exi^rcssion.  In 
reality  these  cases  of  analogy,  homoplasy,  convergence  have  become 
of  supreme  interest  in  our  science.  Their  solution  im])lies  the  greatest 
of  problems,  and  it  is  only  the  thoughtless  orth(xlox  fanatic  who  l)e- 
lieves  that  similarity  in  structure  must  mean  relationship.  To  him 
two  and  two  make  four,  no  matter  what  the  twos  are  composed  of." 

But  most  naturalists  believe  that  homology,  which  involves 
common  descent,  and  analogy,  which  rests  on  similar  exi)eri- 
ences,  are  cpiite  distinct  elements,  and  that  they  can  always 
be  distinguished  bT  recognized  biological  tests. 

No  one  can  c[uestion  the  vast  influence  of  extrinsic  or  en- 
vironmental influences  on  the  history  of  a  species  of  animal  or 
plant.  In  the  analysis  of  such  influences  we  find  a  wide  varit^ty 
of  opinions.  According  to  some  writers,  these  forces  are  dy- 
namic, shaping  the  development  of  the  individual,  and  by 
heredity  determining  through  the  individual  the  future  of  the 
species.     Dall  uses  these  striking  words: 

''The  environment  stands  in  relation  to  the  indivivlual  as  the  ham- 
mer and  anvil  to  the  blacksmith's  lu)t  iron.  The  organism  sutlers 
during  its  entire  existence  a  continuous  series  of  mechanical  impacts, 
none  the  less  real  because  invisible." 


206  EVOLUTION   AND   ANIMAL   LIFE 

Others,  not  questioning  the  reaUty  of  the  direct  effects  of 
environmental  forces  on  the  individual,  find  no  evidence  that 
these  impacts  are  perpetuated  in  heredit}'. 

Besides  direct  effects  of  these  outside  influences,  we  have  to 
consider  an  infinite  variety  of  reactions,  which  these  forces  or 
impacts  may  set  up  in  the  organism.  These  again  have  been 
supposed  to  be  hereditary,  for  the  species  changes  under  them 
in  what  seems  to  be  very  much  the  same  fashion  that  the  indi- 
vidual does.  Use  and  disuse  in  the  species  bring  about  parallel 
results  to  those  shown  by  use  and  disuse  in  the  individual,  ar-d 
are  by  some  therefore  referred  to  the  same  cause. 

But  again  there  is  grave  reason  to  question  the  fact  of  the 
inheritance  of  such  reactions,  and  to  doubt  whether  the  effects 
of  use  and  disuse  in  the  species  rest  on  the  same  set  of  causes  as 
the  results  of  use  and  disuse  in  the  individual. 

There  remains  the  supposition,  adopted  at  least  tentatively 
by  a  large  proportion,  probably  the  majority,  of  the  naturalists 
of  to-day,  that  the  direct  effects  of  environment,  as  well  as  the 
reactions  or  indirect  effects  on  the  individual,  are  not  repeated 
in  heredity,  and  that  the  selective  influence  of  environmental 
causes  is  the  measure  of  their  influence  in  the  transformation  of 
epecies. 

The  question  of  the  nature  of  dynamic  forces  in  evolution  is 
one  of  the  most  recent  and  most  interesting  phases  of  the  long- 
continued  discussion  of  the  inheritance  of  acquired  characters. 

A  vast  range  of  variations  are  ontogenetic,  or  dependent  on 
influences  affecting  directly  the  life  of  the  individual.  These 
ontogenetic  variations  are,  strictly  speaking,  individual,  ap- 
pearing as  collective  only  when  many  individuals  have  been 
subjected  to  the  same  conditions.  They  may  be  divided  into 
environmental  variations  and  functional  variations,  two  cate- 
gories which  cannot  always  be  clearly  separated,  as  variations 
due  to  food  conditions  partake  of  the  nature  of  both. 

More  than  thirty  years  ago.  Dr.  J.  A.  Allen  demonstrated 
that  climatic  influences  affect  the  averages  in  measurements  and 
in  color  among  birds.  For  example,  in  several  species  of  birds, 
the  total  length  is  greater  in  specimens  from  the  north,  while 
the  bills  and  toes  are  actually  longer  in  southern  specimens. 
That  this  condition  is  due  to  the  influence  of  climate  on  develop- 
ment is  apparently  shown  by  the  fact  that  numerous  species  are 
affected  in  the  same  way.     It  is  noticed  also  that   specimens 


INHERITANCE   OF  ACs-JIRED  CHARACTERS  207 


from  the  northeast  and  the  nciihwest  of  tlic  United  States  are 
darker  in  color  than  those  from  the  interior,  and  a^ain  that  red 
shades  are  more  common  in  the  arid  southwest.  Similar  effects 
have  been  recently  sliown  by  a  study  of  species  of  wasps.  .Modi- 
fications of  this  type  may  be  i)roduced  at  will  by  subjecting 
the  larvic  and  pupa)  of  certain  in- 
sects to  artificial  heat  and  cold. 
The  butterflies  of  the  glacial  'regions 
and  those  developed  in  the  ice  chest 
have  a  pale  coloration,  and  a  warm 
environment  deepens  the  pigment. 
The  wood})cckers  and  otlier  birds  of 
the  rainy  forests,  northwest  and 
northeast,  have  ahvays  darker  and 
more  sooty  plumage  than  those  birds 
of  the  same  type  found  in  more 
sunny  regions. 

A  typical  case  is  found  in  the 
various  species  of  sticklebacks  (Fig. 
119)  constituting  the  genera  Gaster- 
osteus  and  Pygosieus  of  the  Northern 
Temperate  Zone.  In  both  genera, 
the  marine  species  are  armed  for  the 
whole  length  of  the  body  by  a  series 
of  about  twenty  to  thirty  vertically 
oblong  enameled  bony  plates. 

In  brackish  waters  in  Europe, 
America,  and  Asia  alike,  the  stickle- 
backs in  all  the  various  species  are 
only  partially  mailed,  having  vari- 
ously from  three  to  fifteen  bony 
plates,  these  smaller  than  in  the 
marine  forms  and  covering  only  the 

anterior  part  of  the  body.  In  these  fishes  also,  the  spines  of 
the  fins  are  less  developed  than  in  the  marine  forms.  In 
strictly  fresh  waters,  sticklebacks  of  various  types  are  found 
entirely  destitute  of  bony  plates.  These  miarmed  fishes  have 
been  regarded  as  distinct  species  and  as  distinct  subspecies. 
At  present  they  are  usually  simply  regarded  as  variant  "  forms," 
to  which  distinctive  scientific  names  need  not  be  api>lied.  It 
has  not  been  proved,  but  it  is  probably  a  fact,  that  the  difTer- 


FiG.  118. — Specimen  of  Cera- 
tium,  collecteil  (A)  out  of  the 
Guincji  Coui^t  stream  and  (B) 
out  of  the  South  Kquatoriai 
stream;  note  the  markeil  dif- 
ference in  development  of  the 
spines,  (.\fter  Weismann  and 
Chun.) 


208 


EVOLUTION   AND   ANIMAL   LIFE 


-lilt-  4  'f '  f  *•  •^i'VLr^  vr^i'*-"'  '*      -^z::^ 


^^ 


'!%    ' 


.^ 


-1 


;-^J 


Fig.  119. — Specimens  of  the  stickleback,  Gasterostus  cataphr actus,  collected  in  different 
kinds  of  water,  and  showing  marked  variations  in  the  number  of  lateral  bony- 
plates  and  in  the  size  of  the  dorsal  fin  rays;  at  the  top,  specimens  collected  in  the 
salt  water  (note  many  lateral  plates  and  large  dorsal  fin  rays);  next  figure  below, 
specimens  collected  in  brackish  water;  next  below,  specimens  collected  in  a  river 
mouth;  at  the  bottom,  specimens  collected  in  a  river,  with  no  lateral  plates  and 
small  dorsal  fin  rays. 


INHERITANCE   OF   ACQUIRED  CHARACTERS  209 

ence  is  one  due  to  the  environment  of  the  in(Hvidual.  Those 
in  the  sea  find  adequate  sahs  from  wliieli  to  devehip  tlicir 
coats  of  mail.  Those  in  fresh  water  do  not  find  this,  while 
those  in  river  mouths  and  otlier  Ijraokish  situations  develop 
armature  in  intermediate  degrees.  In  the  genus  Kucnlia,  a 
sticklel)ack  confined  to  fresh  waters  of  the  Middle  A\'estern 
States,  plates  are  never  developed. 

The  Loch  Leven  trout,  Salmo  levenensis,  is  distinguished 
from  the  brook  trout  of  England,  Salmo  eriox  {jario),  in  its 
native  waters  by  certain  o])vious  characters.  These  disappear 
when  the  eggs  are  planted  in  brooks  in  England  or  in  Cahfornia, 
and  the  species  develops  as  the  common  English  brook  trout. 
But  it  is  conceivable  that  the  obvious  or  ontogenetic  traits  of 
the  Loch  Leven  trout  are  not  the  real  or  phylogenetic  distinc- 
tions, and  that  the  latter,  more  subtle,  engendered  through  in- 
dividual variation,  inheritance,  selection,  and  isolation,  really 
exist,  although  they  have  escaped  the  attention  of  iclithy- 
ologists. 

After  the  Loch  Leven  trout  was  planted  in  the  Yosemite 
Park  in  1896,  it  remained  for  nine  years  unnoticed.  In  19U5 
individuals  sent  to  Stanford  University  wef^,  so  far  as  could 
be  seen,  exactly  like  English  brook  trout.  But  it  is  conceivable 
that  differences  in  food  and  water  have  caused  slight  ontogenetic 
distinctions.  It  is  certain  that  in  isolation  from  all  parent 
stocks  they  will  in  time  develop  larger  differences  which,  after 
many  thousand  generations,  will  be  specific  or  subspecific.  At 
present,  these  trout  are  quite  unlike  the  native  rainbow  trout 
{Salmo  irideus  gilherti)  of  the  Yosemite.  The  ontogenetic  char- 
acters will  perhaps  approach  those  of  the  latter,  but  the  phylo- 
genetic movement  may  be  in  quite  another  direction. 

Another  ontogenetic  species  is  the  little  char  or  trout  {Sal- 
velinus  tudes  Cope)  from  Unalaska.  In  Captain's  Harbor,  Una- 
laska,  the  Dolly  Varden  trout,  Salveliiius  malma,  swarms  in 
myriads,  in  fresh  and  salt  water  alike,  reaching  in  the  sea  a 
weight  of  from  six  to  twelve  pounds.  A  little  oj)en  brook,  whicli 
drops  into  the  harbor  by  an  impassable  waterfall,  contains  also 
an  abundance  of  Dolly  Varden  trout,  mature  at  six  inches  and 
weighing  but  a  few  ounces.  This  is  Salvelinus  tudcfi.  In  the 
harbor  the  trout  are  gray  with  lighter  gray  sjiots,  and  fins  scarcely 
rosy.  In  the  brook,  the  trout  are  steel  blue,  with  crimson  spots 
and  orange  fins,  striped  with  white  and  black.     In  all  visible 


210  EVOLUTIOX   AND   ANIMAL   LIFE 

phylogenetic  characters,  the  two  forms  of  trout  are  one  species. 
We  have  reason  to  beheve  that  fry  from  the  bay  would  grow  up 
as  dwarfs  in  the  brook,  and  that  the  fr}^  from  the  brook  would  be 
gray  giants  if  developed  in  the  sea. 

But  it  is  also  supposable  that  in  the  complete  isolation  of  the 
brook  fishes,  with  free  interbreeding,  there  would  be  some  sort 
of  phylogenetic  bond.  There  may  be  a  genuine  subspecies, 
tildes,  characterized  not  by  small  size,  slender  form,  and  bright 
colors,  but  by  other  traits,  which  no  one  has  found  because  no 
one  has  looked  deeply  enough. 

In  no  group  of  vertebrates  are  the  life  characters  more  plastic 
than  among  the  trout.  The  birds  have  traits  far  more  definitely 
fixed.  Yet  differences  in  external  conditions  must  produce  cer- 
tain results.  We  should  not  venture  to  suggest  that  the  dusky 
woodpeckers  or  chickadees  of  the  rainy  forests  of  the  northeast 
and  northwest  are  purely  ontogenetic  species  or  that  they  should 
be  erased  from  the  systematic  lists.  But  it  will  be  a  great  ad- 
vance in  ornitholog}^  when  we  know  what  they  really  are  and 
when  we  understand  the  real  nature  of  the  small-bodied,  large- 
billed,  southern  races  of  other  species  of  birds.  It  would  be 
worth  while  to  know  if  these  are  really  ontogenetic  purely,  or 
if  they  are  phylogenetic  through  "progressive  heredity,"  the 
inheritance  of  acquired  characters,  such  as  are  produced  by 
the  direct  effects  of  climate  or  as  the  reaction  from  climatic 
influences.  Or  again  may  there  be  a  real  phylogenetic  bond 
through  geographical  segregation,  its  evidences  obscured  by 
the  more  conspicuous  traits  induced  by  like  experiences?  Or 
are  there  other  influences  still  more  subtle  involved  in  the 
formation  of  isohumic  or  isothermic  subspecies? 

To  sum  up,  there  is  no  convincing  evidence  that  the  direct 
influence  of  environment  is  a  factor  in  the  separation  of  species, 
except  as  its  results  may  be  acted  upon  b}^  natural  selection. 
We  have  no  proof  to  show  that  the  environment  of  one  genera- 
tion determines  the  heredity  of  the  next — and  yet  perhaps 
most  naturalists  feel  that  the  effects  of  extrinsic  influences  work 
their  way  into  the  species,  although  a  mechanism  by  which 
this  might  be  accomplished  is  as  yet  uriknown  to  \;s, 


CHAPTER  XII 
GENERATION,   SEX  AND   ONTOGENY 

"Unter  jedem  Grab  liegt  eine  Weltgeschichte  "  ((lernuin  i)rovcrb). 

Each  animal,  each  plant,  must  have  its  individual  l)('<;inniii^, 
its  "creation/'  and  its  individual  development  from  this  ])egin- 
ning  to  a  full  grown,  complete!}^  developed  condition.  For  no 
organism  is  born  fully  developed.  Even  the  sim})lest  organ- 
isms, the  one-celled  kinds,  whose  "creation"  is  accomplished 
simply  by  the  splitting  in  two  of  a  previously  existing  individual 
of  their  kind,  are  not  produced  full-fledged.  They  have  at 
least  to  increase  from  half  size  to  full  size,  that  is,  to  grow,  and 
there  are  very  few  if  any  of  them  that  do  not  have  to  effect 
changes  in  their  body  structure  during  this  period  of  growth; 
that  is,  they  have  to  undergo  some  development.  The  begin- 
ning, then,  is  always  from  a  previously  existing  organism — but 
how  could  it  always  have  been? — and  between  this  beginning 
and  the  normal  mature  or  full-fledged  creature  there  has 
always  to  be  some  development.  The  beginning  is  called 
generation;  the  development,  ontogeny. 

We  are  all  so  familiar  with  the  fact  that  a  kitten  comes  into 
the  world  only  through  being  born  as  the  offs})ring  of  parents 
of  its  kind,  that  we  shall  likely  not  appreciate  at  first  the  full 
significance  of  the  statement  that  all  life  comes  from  life;  that 
aD  organisms  are  produced  by  other  organisms.  Xor  shall  we 
at  first  appreciate  the  importance  of  the  statement.  This  Ls  a 
generalization  of  modern  times.  It  has  always  been  easy  to  see 
that  cats  and  horses  and  chickens  and  the  other  animals  we 
familiarly  know  give  birth  to  j^oung  or  new  animals  of  their  own 
kind;  or,  put  conversely,  that  young  or  new  cats  and  horses  and 
chickens  come  into  existence  only  as  the  offspring  of  parents 
of  their  kind.     And  in  these  latter  days  of  microscopes  and 

211 


212  EVOLUTION   AND  AXIMAL  LIFE 

mechanical  aids  to  observation  it  is  also  easy  to  see  that  the 
smaller  animals^  the  microscopic  organisms,  come  into  ex- 
istence only  as  they  are  produced  by  the  division  of  other  similar 
animals,  which  we  may  call  their  parents.  But  in  the  days  of 
the  earlier  naturalists  the  life  of  the  microscopic  organisms, 
and  even  that  of  many  of  the  larger  but  unfamiliar  animals, 
was  shrouded  in  mystery.  And  what  seem  to  us  ridiculous 
beliefs  were  held  regarding  the  origin  of  new  individuals. 

The  ancients  believed  that  many  animals  were  spontane- 
ously generated.  The  early  naturahsts  thought  that  flies 
arose  by  spontaneous  generation  from  the  decaying  matter  of 
dead  animals;  from  a  dead  horse  come  myriads  of  maggots 
which  change  into  flesh  flies.  Frogs  and  many  insects  were 
thought  to  be  generated  spontaneously  from  mud.  Eels  were 
thought  to  arise  from  the  shme  rubbed  from  the  skin  of  fishes. 
Aristotle,  the  Greek  philosopher,  who  was  the  greatest  of  the 
ancient  naturahsts,  expresses  these  behefs  in  his  books.  It 
was  not  until  the  middle  of  the  seventeenth  century — Ai'istotle 
lived  three  hundred  and  fifty  years  before  the  Christian  era — 
that  these  behefs  were  attacked  and  began  to  be  given  up.  In 
the  beginning  of  the  seventeenth  century,  William  Harvey,  an 
English  naturalist,  declared  that  every  animal  comes  from  an 
egg,  but  he  said  that  the  egg  might  "proceed  from  parents  or 
arise  spontaneously  or  out  of  putrefaction.^'  In  the  middle  of 
the  same  century  Redi  proved  that  the  maggots  in  decaying 
meat  which  produce  the  flesh  flies  develop  from  eggs  laid  on  the 
meat  by  flies  of  the  same  kind.  Other  zoologists  of  this. time 
were  active  in  investigating  the  origin  of  new  individuals.  And 
all  their  discoveries  tended  to  weaken  the  belief  in  the  theory 
of  spontaneous  generation. 

Finally,  the  adherents  of  this  theory  w^ere  forced  to  restrict 
their  belief  in  spontaneous  generation  to  the  case  of  a  few  kinds 
of  animals,  like  parasites  and  the  animalcules  of  stagnant  water. 
It  was  maintained  that  parasites  arose  spontaneously  from  the 
matter  of  the  living  animal  in  which  they  lay.  Many  parasites 
have  so  complicated  and  extraordinary  a  life  history  that  it  was 
only  after  long  and  careful  study  that  the  truth  regarding  their 
origin  was  discovered.  But  in  the  case  of  every  parasite  whose 
life  history  is  known,  the  young  are  offspring  of  parents,  of 
other  individuals  of  their  kind.  No  case  of  spontaneous  genera- 
tion among  jjarasites  is  known. 


GENERATIOX,  SEX  AND  ONTOGEXY       213 

The  same  is  true  of  the  animalcules  of  stagnant  water.  If 
some  water  in  which  there  are  apparently  no  living  organisms, 
however  minute,  be  allowed  to  stand  for  a  few  days,  it  will  come 
to  be  swarming  Avith  microscoi)ic  plants  and  animals.  Any 
organic  liciuid,  as  a  broth  or  a  vegetable  infusion  exposed  for 
a  short  time,  becomes  foul  through  the  presence  of  innumerable 
bacteria,  infusoria,  and  other  one-celled  animals  and  plants, 
or  rather  through  the  changes  produced  by  tlieir  life  processes. 
But  it  has  been  certainly  proved  that  these  oiganisms  are  not 
spontaneous^  produced  by  the  water  or  organic  licjuid.  A  few 
of  them  enter  the  water  from  the  air,  in  which  there  are  always 
greater  or  less  numbers  of  spores  of  microscopic  organisms. 
These  spores  (embryo  organisms  in  the  resting  stage)  germinate 
quickly  when  they  fall  into  water  or  some  oi-ganic  liquid,  and 
the  rapid  succession  of  generations  soon  gives  rise  to  the  hosts 
of  bacteria  and  Protozoa  which  infest  all  standing  water.  If 
all  the  active  organisms  and  inactive  spores  in  a  glass  of  water 
are  killed  by  boiling  the  water,  "sterilizing"  it,  as  it  is  called, 
and  this  sterilized  w^ater  or  organic  liquid  be  put  into  a  sterilized 
glass,  and  this  glass  be  so  well  closed  that  germs  or  spores  can- 
not pass  from  the  air  wdthout  into  the  sterilized  hquid,  no  living 
animals  will  ever  appear  in  it.  It  is  now"  known  that  flesh  will 
not  -decay  or  liquids  ferment  except  througli  the  presence  of 
living  animals  or  plants.  To  sum  up,  we  may  say  that  we  know 
of  no  instance  of  tlie  spontaneous  generation  of  organisms,  and 
that  all  the  animals  w^hose  life  history  we  know  are  jiroduced 
from  other  animals  of  the  same  kind.  "Owne  vivum  ex  vivo," 
"Ah  life  from  lifc.^^ 

The  method  of  simple  fission  or  sphtting — binary  fission  it 
is  often  called,  because  the  division  is  always  in  two — b}'  which 
the  body  of  the  parent  becomes  divided  into  two  equal  i)arts 
— into  halves — is  the  simplest  method  of  nuiltiplication.  This 
is  the  usual  method  of  Amaba  (Fig.  120)  and  of  many  other  of 
the  simplest  animals.  In  this  kind  of  re})ro(hiction  it  is  hardly 
exact  to  speak  of  parent  and  children.  The  children,  the  new 
Amoibce,  are  simi)ly  the  parent  cut  into  halves.  The  ])arent 
persists;  it  does  not  produce  offspring  an«l  di(\  Its  whole  body 
continues  to  live.  The  new  Amabte  take  in  and  assimilate  food 
and  add  new"  matter  to  the  original  matter  of  the  parent  body; 
then  each  of  them  divides  in  two.  The  grand])arent's  body  is 
now  divided  into  four  parts,  one  fourth  of  it  forming  one  half 
15 


214 


EVOLUTION  AND  ANIMAL  LIFE 


of  each  of  the  bodies  of  the  four  grr.nclchildren.  The  process 
of  assimilation,  growth,  and  subsequent  division  takes  place 
again  and  again  and  again.  Each  time  there  is  given  to  the 
new  Amoeba  an  eA^er-lessening  part  of  the  actual  body  substance 
of  the  original  ancestor.     Thus  an  Amoeba  never  dies  a  natural 


Fig.  120. — A  multiplication  of  Amoeba  by  simple  fission. 


death,  or,  as  has  been  said,  "no  Amoeba  ever  lost  an  ancestor 
by  death.''  It  may  be  killed  outright,  but  in  that  case  it  leaves 
no  descendants.  If  it  is  not  killed  before  it  produces  new 
Amoebce  it  never  dies,  although  it  ceases  to  exist  as  a  single 
individual.  The  Amoebce  and  other  simple  animals  which 
multiply  by  direct  binary  fission  may  be  said  to  be  immortal, 
and  the  "  immortality  of  the  Protozoa  "  is  a  phrase  w^hich  will 


GENERATION,   SEX   AND   ONTOGENY 


215 


Fig.  121. — Stentor  reproducing  hy  fission. 
(After  Stein.) 


often  be  met  with  in  the  writings  of  Weismann  and  certain  other 

modern  })liilosophical  biologists.     There  is  a  faUacy,  liowever, 

in  the  phrasing,  l^ecaiise, 

as  a  matter  of  fact,  the  "^  > 

protoplasm    of    a    given 

protozoon  gradually  loses 

its  vitality  with  con- 
tinued   division    until    it 

ultimately   is    unable    to 

divide  further  or  indeed 

to  perform  the  other  life 

functions:  it   dies  of  old 

age. 

Hardly  less  simple  is 

generation    by    budding, 

Avliich     in     its     simplest 

character  is  the  breaking 

off   from  one   individual 

of  a  part  smaller  than  a 

half,   often,  indeed,  only 

a  very  small  fractional  part,  which  budded  off  ])art  has  the 

capacity  of  growing  and  developing  into  a  new  individual  like 

its  parent. 

A  still  other 
mode  of  generation 
of  simple  type  is 
that  of  sporulalion, 
or  where  the  l)ody 
of  one  individual 
subdivides  into 
more  than  two 
l)arts  (as  in  binary 
fission),  these  parts, 
each  of  wliich  is 
usually  sul)spherical 
or  ellipsoidal  num- 
bering ])  e  r  h  a  [>  s 
many  Inuidreds. 
A   condition   known   as    parlhcjwgcncsis   is   foimd    amont^ 

certain  of  the  complex  animals.     Allliough  the  species  is  repre- 
sented by  individuals  of  both  sexes,  the  female  can  produce 


Fig.  122. — Holophrya  nuiUifdiis,  an  infusorian  parasitic 
on  fishes  reproducing  by  sporulalion. 


216 


EVOLUTION   AXD   ANIMAL    LIFE 


B 


young  from  eggs  which  have  not  been  fertihzed.  For  example, 
the  queen  bee  lays  both  fertilized  and  unfertilized  eggs.  From 
the  fertilized  eggs  hatch  the  workers,  which  are  rudim.entary 
females,  and  other  ciueens,  which  are  fully  developed  females; 
from  the  unfertilized  eggs  hatch  only  males — the  drones. 
Many  generations  of  plant  lice  are  produced  each  j^ear  parthe- 
nogenetically — that  is,  by  unfertilized  females.     This  subject 

will  be  discussed  at 
greater  length  later 
in  this  chapter. 

The  modes  of 
generation,  or  re- 
production, or  mul- 
tiplication, as  this 
the  begin- 
of  new  indi- 
viduals may  be 
variously  called,  so 
far  referred  to,  may 
be  grouped  into  a 
category  called  asex- 
ual  generation. 
In  an  examination 
of  tlie  lives  of  the 
simplest  and  but 
slightly  complex 
kinds  of  animals  we 
find  that  even 
among  almost  the 
very  simplest  of  or- 


making 
nings 


Fig.  123. — Gregarinida?.  A,  A  gregarimd,^c^mocepAa7?/s 
oligacanthus,  from  the  intestines  of  an  insect  (after 
Stein);  B  and  C,  spore-forming  bj^  a  gregarinid,  Coc- 
cidium  ovifornie,  from,  liver  of  a  guinea-pig  (after  Lexie- 
kart);  D,  E,  and  F,  successive  stages  in  conjugation  of 
spore-forming  by  Gregarina  polymorpha.  (After  Kol- 
liker.) 

ganisms  another 
mode  of  reproduction  obtains,  at  least  occasionally,  which 
demands  for  its  carrying  out  the  mutual  action  of  two  distinct 
individuals.  The  essential  thing  in  this  mutual  action  is  the 
exchange  of  nuclear  material  from  one  of  these  individuals  to 
the  other;  with  some  of  the  simplest  organisms  there  is  a  mutual 
exchange  of  nuclear  material. 

Paramoecmm.,  for  example,  reproduces  itself  for  many  gen- 
erations by  fission,  but  a  generation  finally  appears  in  which 
a  different  method  of  reproduction  is  followed.  Two  individu- 
als come  together  and  each  exchanges  with  the  other  a  part  of 


GENERATIOX,  SEX  AM  J  UXTOGEX\        217 

its  nucleus.  Then  the  two  individuals  separate  and  cacli 
divides  into  two.  I'he  result  of  this  conjugation  is  to  give  to 
the  new  P«ra???ffrm- produced  by  the  conjugating  individuals 
a  body  wliicli  contains  part  of  the  body  substance  of  two  distinct 
individuals.  The  new  Paramacia  arc  not  simply  halves  of  a 
single  parent,  they  are  parts  of  two  parents. 

Among  tlic  colonic!  Protozoa  the  first  differentiation  of 
the  cells  or  mom])ers  comi)osing  the  colony  is  the  difTerentia- 
tion  into  two  kinds  of  iei)roductive  cells.  Reproduction  by 
cimple  division,  without  i)receding  conjugation,  c^n  and  does 
take  i)lace,  to  a  certain  extent,  among  all  the  coloniid  Protozoa. 
Indeed,  this  simple  method  of  multii)li('a(ion,  or  some  modi- 
fication of  it,  like  l)udding,  persists  auKjng  many  of  the  com- 
plex animals,  as  the  sponges,  the  polyps,  r.nd  even  higher  and 
more  complex  forms.  But  such  a  method  of  single-parent 
reproduction  cannot  be  used  alone  by  a  species  for  many  gener- 
ations, and  those  animals  which  possess  the  j)Ower  of  nuiltiplica- 
tion  in  this  way  always  exhibit  also  the  other  more  comj)lex 
kind  of  multiplication,  the  method  of  doul)le-])arent  re])ro(luc- 
tion.  Conjugation  takes  place  between  different  meml)ers  of 
a  single  colony  of  one  of  the  colonial  Protozoa,  or  between 
members  of  different  colonies  of  the  same  species.  These 
conjugating  individuals  in  the  simpler  kinds  of  colonies,  like 
Gonium,  are  similar;  in  Pandoriim  they  apjiear  to  be  slightly 
different,  and  in  Eudorina  and  ^^olvox  the  conjugating  cells  are 
readily  seen  to  be  very  different  from  each  other.  One  kind  of 
cell,  which  is  called  the  egg  cell,  is  large,  spherical,  and  inactive, 
wliile  the  other  kind,  the  sperm  cell,  is  small,  with  (n-oid  head 
and  tapering  tail,  and  free-swimming.  In  the  simpler  colo- 
nial Protozoa  all  the  cells  of  the  body  take  piirt  in  reproduction, 
but  in  ]^olvox  only  certain  cells  i)erform  this  function,  and  the 
other  cells  of  the  bodv  die.  Or  we  may  sav  that  the  bodv  of 
Volvox  dies  after  it  has  ])roduced  sjiecial  reproductive  cells 
which  shall  fulfill  the  function  of  multii)lication. 

Beginning  with  the  more  comi)lex  ]'olvocinu\  whicli  we 
may  call  either  the  moat  complex  of  the  one-celled  animals  or 
the  simplest  of  the  many-celled  animals,  all  the  complex 
animals  show  this  distinct  differentiation  between  the  rei>ra- 
ductive  cells  and  the  cells  of  the  rest  of  the  body.  Of  course, 
we  find,  as  soon  as  we  go  up  at  nil  far  in  the  scale  of  the  animal 
world,  that  there  is  a  great  deal  of  differentiation  among  the 


218 


EVOLUTION  AXD  ANIMAL  LIFE 


cells  of  the  body:  the  cells  which  have  to  do  with  the  assimila- 
tion of  food  are  of  one  kind;  those  on  which  depend  the  motions 
of  the  body  are  of  another  kind;  those  which  take  ox3^gen  and 
those  which  excrete  waste  matter  are  of  other  kinds.  But 
the  first  of  this  cell  differentiation,  as  we  have  ah-eady  often 
repeated,  is  that  shown  by  the  reproductive  cells;  and  with 
the  very  first  of  this  differentiation  between  reproductive  cells 
and  the  other  body  cells,  appears  a  differentiation  of  the  re- 


FiG.  124. — Spermatozoa  of  different  animals:  1,  IMan;  2,  Vesperugo;  3,  pig;  4,  rat; 
5,  finch;  6,  triton;  7,  ray;  8,  beetle;  9,  mole  cricket;  10,  snail.  (After  Ballowitz, 
KoUiker,  and  Rath.) 


productive  cells  into  two  kinds.  These  two  kinds,  among  all 
animals,  are  alwavs  essentiallv  similar  to  the  two  kinds  shown 
by  Volvox  and  the  simplest  of  the  many-celled  animals — 
namely,  large,  inactive,  spherical  egg  cells,  and  small,  active, 
elongate  or  "  tailed  '^  sperm  cells. 

In  the  slightly  complex  animals  one  individual  produces 
both  egg  cells  and  sperm  cells.  But  in  the  Siphonophora,  or 
colonial  jelly  fishes,  certain  members  of  the  colony  produce  only 
sperm  cells,  and  certain  other  members  of  the  colony  produce 
only  egg  cells.  If  the  Siphonophora  be  considered  an  indi- 
vidual organism  and  not  a  colony  composed  of  many  Individ- 


GENERATIOX,  SEX. AND  OXTOGEXY 


219 


uals,  then,  of  course,  it  is  like  the  others  of  the  shghtly  com- 
plex animals  in  this  respect.     But  as  soon  as  we  rise  higher  in 


c 


^^^r#* 


t. 


^^*^'^s^ 


Fig.  125. — Fertilization  of  Petromyzon  fluvial  His:  A,  Sperm  nucleus  in  periphery  of  the 
egg  plasm;  B,  yperm  nucleus  in  periphery  of  the  egg  plasm.  an«l  egg  nucleus  ap- 
proaching; C-E,  fusing  of  the  ogg  and  .-iktiu  nuclei,  and  appearance  of  the  alters; 
F,  cleavage  of  nucleus.     (After  llcrfort.) 


the  scale  of  animal  life,  as  soon  as  we  study  the  more  comjlex 
animals,  we  find  that  the  egg  cells  and  sperm  cells  arc  almost 


220 


EVOLUTION   AND   ANIMAL   LIFE 


always  produced  by  different  individuals.  Those  individuals 
which  produce  egg  cells  are  called  female,  and  those  which 
produce  sperm  cells  are  called  male.  There  are  two  sexes. 
Male  and  female  are  terms  usually  applied  onl}^  to  individ- 
uals, but  it  is  evidently  fair  to  call  the  egg  cells  the  female 
reproductive  cells,  and  the  sperm  cells  the  male  reproductive 
cells.  A  single  individual  of  the  simpler  kinds  of  animals 
produces  both  male  and  female  cells.  But  such  an  individual 
cannot  be  said   to   be   either  male  or  female,  it  is  sexless — 

that  is,  sex  is  some- 
thing which  appears 
only  after  a  certain 
degTee  of  structural 
and  phj^siological 
differentiation  is 
reached.  It  is  true 
that  even  among 
many  of  the  higher 
or  complex  animals 
certain  species  are 
not  represented  by 
male  and  female  in- 
diiaduals,  any  indi- 
vidual of  the  species 
being  al^le  to  pro- 
duce both  male  and 
female  cells.  But 
this  is  the  exception. 
Among  almost  all  the  complex  animals  it  is  necessary  that 
there  be  a  conjugation  of  male  and  female  reproductive  cells 
in  order  that  a  new  individual  may  be  produced.  This  neces- 
sity first  appears,  we -remember,  among  very  simple  animals. 
This  intermixing  of  bod}^  substance  from  two  distinct  indiAdduals 
and  the  development  therefrom  of  the  new  individual  is  a 
phenomenon  which  takes  place  through  the  whole  scale  of 
animal  life.  The  object  of  this  intermixing  seems  to  be  the 
production  of  variation;  at  least  it  Avould  seem  that  variation 
must  result  from  such  a  mode  of  generation.  By  having  the 
beginnings  of  an  organism's  body,  the  single  cell  from  which 
this  whole  body  develops,  composed  of  parts  of  two  different 
individuals,  a  difference  between  the  offspring  and   the  par- 


FiG.  126. — Conjugation  of  Noctiluca,  a  one-celled  ani- 
mal: A,  Two  individuals  just  fusing;  B,  the  same 
with  cytoplasm  wholly  fused  and  nuclei  lying  closely 
together;  C,  the  two  nuclei  in  closer  fusion;  D,  the  be- 
ginning of  fission.      (After  Ischikawa.) 


GENERATION,   SEX   AND   ONTOGENY 


221 


ents,  although  it  may  be  shght  and  imporoeptiblo,  is  in- 
sured. Sex  is  a  condition  of  nature  whicli  is  one,  at  least, 
of  the  causes  of  variation. 


Fig,  127. — Conjugation  of  the  infusorian,  Vorfiyella  nebnUfern;  the  smaller  imlividiial 
at  the  right  may  be  regarded  as  the  male,     (.\ftor  Weismann.) 

As  we  have  seen,  almost  every  species  of  animal  is  repre- 
sented by  two  kinds  of  individuals,  males  anrl  females.  In  tlie 
case  of  many  animals,  especially  the  simpler  ones,  these  two 


^K9W 


J^ 


't 


■4 


ilij.    1J5. — .Mali.'   l)ir<i  til    ii;iiaili>L'. 


kinds  of  individuals  may  not  differ  in  a):)i")earance  or  in  structure 
apart  from  tlie  organs  concerned  witli  nniltij^hcation.  But 
with  many   animals   the  sexes   can   be  readily  distinguislied. 


222 


EVOLUTION  AND  ANIIMAL  LIFE 


The  male  and  female  individuals  often  show  marked  differences, 
especially  in  external  structural  characters.  We  can  readily 
tell  the  peacock,  with  its  splendidly  ornamental  tail  feathers, 
from  the  unadorned  peafowl,  or  the  horned  ram  from  the 
bleating  ewe.  There  is  here,  plainly,  a  dimorphism — the 
existence  of  two  kinds  of  individuals  belonging  to  a  single 
species.  This  dimorphism  is  due  to  sex,  and  the  condition 
may  be  called  sex  dimorphism.  Among  some  animals  this  sex 
dimorphism,  or  difference  between  the  sexes,  is  carried  to  ex- 
traordinary extremes.     This  is  especially  true  among  polyga- 


FiG.  129. — Cankerworm  moth:   the  winged  male  and  wingless  female. 


mous  animals,  or  those  in  which  the  males  mate  with  many 
females,  and  are  forced  to  fight  for  their  possession.  The  male 
bird  of  paradise,  with  its  gorgeous  display  of  brilliantly  colored 
and  fantastically  shaped  feathers  (Fig.  128),  seems  a  wholl)^ 
different  kind  of  bird  from  the  modest  brown  female.  The 
male  golden  and  silver  pheasants,  and  allied  species  with  their 
elaborate  plumage,  are  very  unlike  the  dull-colored  females. 
The  great,  rough,  warlike  male  fur  seal,  roaring  like  a  lion^  is 
three  times  as  large  as  the  dainty,  soft-furred  female,  which 
bleats  like  a  sheep. 

Among  some  of  the  lower  animals  the  differences  between 
male  and  female  are  even  greater.  The  males  of  the  common 
cankerworm  moth  (Fig.  129)  have  four  wings;  the  females  are 
wingless,  and  several  other  insect  species  show  this  same 
difference.  Among  certain  species  of  white  ants  the  females 
grow  to  be  five  or  six  inches  long,  while  the  males  do  not  ex- 
ceed half  an  inch  in  length.  In  the  case  of  some  of  the  para- 
sitic worms  which  live  in  the  bodies  of  other  animals  the  male 
has  an  extraordinarily  degraded,  simple  body,  much  smaller 


GENERATION,  SEX  AND  ONTOGENY 


223 


than  that  of  the  female  and  differinf^  greatly  from  it  in  structure. 
In  some  cases  even — as,  for  example,  the  worm  which  causes 
"gapes"  in  cliickens — the  male  hvcs  ])arasitically  on  tlie  female, 
being  attached  to  her  body  for  its  whole  lifetime,  and  draw- 
ing its  nourishment  from  her  blood  (I'ig.  I'M)). 

Some  of  the  complex  animals  are  hcrmaphrodUic — that  is, 
a  single  individual  produces  both  egg 
cells  and  sperm  cells.  The  tapeworm 
and  many  allied  worms  show  this  con- 
dition. This  is  the  normal  condition  for 
the  simplest  animals,  as  we  have  already 
learned,  but  it  is  an  exceptional  condition 
among  the  complex  animals. 

However  the  beginnings  of  the  new 
organisms  are  produced,  whether  asexu- 
ally  or  bisexually  (whether,  that  is,  by 
simple  division,  budding,  sporulation,  or 
as  true  but  unfertilized  eggs,  or  as  eggs 
with  a  nucleus  made  by  the  fusion  of  two 
germinal  nuclei  from  male  and  female  in- 
dividuals respectively,  or  from  an  her- 
maphroditic individual) ,  this  new  organism 
in  embryo  has  a  shorter  or  longer  course 
of  development  and  growth  to  undergo, 
before  it,  in  turn,  is  in  condition  to  pro- 
duce new  individuals  of  its  kind. 

Certain  phenomena,  are  familiar  to  us 
as  recurring  inevitably  in  the  life  of  every 
animal  which  we  familiarly  know.  Each 
individual  is  born  in  an  immature  or 
young  condition;  it  grows  (that  is,  it  in- 
creases in  size)  and  develops  (that  is, 
changes  more  or  less  in  structure)  and  dies, 
occur  in  the  succession  of  birth,  growth,  and  development,  and 
death.  But  before  any  animal  ai^i^jears  to  us  as  an  independc" 
individual— that  is,  outside  the  body  of  the  mother  and  outside 
of  an  egg  (i.  e.,  before  birth  or  hatcliing,  as  we  are  accustomed 
to  call  such  appearance) — it  has  already  undergone  a  longer 
or  shorter  period  of  life.  It  has  been  a  new  living  organism 
hours  or  days  or  montlis,  perhaps,  ])efore  its  aj^iK'nrance  to  us. 
This  period  of  life  has  been  passed  inside^  an  egg.  or  as  an  egg, 


Fig.  130. — The  parasitic 
worm,  Syngamua  trache- 
alis,  which  causes  tlie 
gapes  in  fowls.  The 
male  is  attachetl  to 
the  female  and  Uvea 
as  a  parasite  on  her. 

These  ])henomena 


224 


EVOLUTION    AND  ANIMAL  LIFE 


or  in  the  egg  stage,  as  it  is  variously  termed.  The  hfe  of  an 
animal  as  a  distinct  organism  begins  in  an  egg.  And  the  true 
life  cycle  of  an  organism  is  its  life  from  egg  through  birth,  growth 
and  development  and  maturity  to  the  time  it  produces  new 
organisms  in  the  condition  of  eggs.  The  life  cycle  is  from 
egg  to  egg.  Birth  and  growth,  two  of  the  phenomena  readily 
apparent  to  us  in  the  life  of  every  animal,  are  two  phenomena 


Fig.  131. — Leptodera  hyalina,  showing  sex  dimorphism:    A,  Head  of  male;   B,  head  of 

female. 


in  the  true  life  cycle.  Death  is  a  third  inevitable  phenomenon 
in  the  life  of  each  individual,  but  it  is  not  a  part  of  the  cycle; 
it  is  something  outside. 

The  single  cell  formed  by  the  fusion  of  two  germ  cells  is 
called  a  fertilized  egg  cell,  and  its  subsecjuent  development 
results  in  the  formation  of  a  new  individual  of  the  same  species 
with  its  parents.  Now,  in  the  development  of  this  cell  into 
a  new  animal,  food  is  necessary.  So  with  the  fertilized  egg 
cell  there  is,  in  the  case  of  most  animals  th.at  lay  eggs,  a  greater 
cr  less  amount  of  food  matter — food  yolk,  it  is  called — gath- 
ered about  the  germ  cell,  and  both  germ  cell  and  food  yolk 
are  inclosed  in  a  soft  or  hard  wall.  Thus  is  composed  the 
egg  as  we  know  it.  The  hen's  egg  is  as  large  as  it  is  because 
of  the  great  amount  of  food  yolk  it  contains.  The  egg  of  a 
fish  as  large  as  a  hen  is  much  smaller  than  the  hen's  egg;  it 
contains .  less  food  yolk.  Eggs  (Fig.  132)  ma}^  vary  also  in 
their  external  appearance,  because  of  the  different  kinds  of 
membrane  or  shells  which  may  inclose  and  protect  them. 
Thus  the  frog's  eggs  are  inclosed   in  a  thin   membrane   and 


GENERATION,   SEX   AND   ONTOGENY 


225 


imbedded  in  a  soft,  jellylikc  substance;  the  skate's  egg  has  a 
tough,  dark-brown  leathery  inclosing  wall;  tlie  spiral  egg  of 
the  bullhead  shark  is  leathery  and  colored  hke  the  dark-olive 
seaweeds  among  which  it  lies;  and  a  bird's  egg  has  a  hard 
shell  of  carbonate  of  lime.  But  in  each  case  there  is  the  essen- 
tial fertilized  germ  cell;  in  this  the  eggs  of  hen  and  fish  and 
butterfly  and  crayfish  and  worm  are  alike,  however  much  they 
may  differ  in  size  and  external  appearance. 

There  is  great  variation  in  the  number  of  young  ])roduccd  by 
different  species  of  animals.  Among  the  animals  we  know 
familiarly,  as  the  mammals,  which  give  birtli  to  young  ahve, 


Fig,  132. — Eggs  of  different  animals  shov.ing  variety  in  cxternaJ  api>earanco :  a,  Egg 
of  bird;  h,  eggs  of  toad;  c,  egg  of  fish;  rf.egg  of  butterfly;  e,  eggs  of  katydid  on  leaf; 
/,  egg  case  of  skate. 

and  the  birds,  which  lay  eggs,  it  is  the  general  rule  that  but 
few  young  are  produced  at  a  time,  and  the  young  are  born  or 
eggs  are  laid  only  once  or  perhaj^s  a  few  ti  nes  in  a  year.  The 
robin  la^^s  five  or  six  eggs  once  or  twice  a  year;  a  cow  may 
produce  a  C^lf  each  year.    Rabbits  ai  J   i>igeori?  are  more 


226 


EVOLUTION   AND   ANIMAL   LIFE 


prolific,  each  having  several  broods  a  year.  But  when  we  ob- 
serve the  multiplication  of  some  of  the  animals  whose  habits 
are  not  so  familiar  to  us,  we  find  that  the  production  of  so  few 
young  is  the  exceptional  and  not  the  usual  habit.  A  lobster 
lays  ten  thousand  eggs  at  a  time;  a  queen  bee  lays  about  five 

million  eggs  in  her  life  of  four  or  five  years. 
A  female  termite  of  a  certain  species,  after  it  is 
full  grown,  does  nothing  but  lie  in  a  cell  and 
lay  eggs,  producing  eighty  thousand  eggs  a  day 
steadily  for  several  months.  A  large  codfish 
was  found  on  dissection  to  contain  about  eight 
million  eggs. 

If  we  search  for  some  reason  for  this  great 
difference  in  fertility  among  different  animals, 
we  may  find  a  promising  clew  by  attending 
to  the  duration  of  life  of  animals,  and  to  the 
amount  of  care  for  the  young  exercised  by 
the  parents.  We  find  it  to  be  the  general  rule 
that  animals  which  live  many  years,  and  which 
take  care  of  their  young,  produce  but  few 
young;  while  animals  which  live  but  a  short 
time,  and  w^hich  do  not  care  for  their  young, 
are  very  prolific.  The  codfish  produces  its  mil- 
lions of  eggs;  thousands  are  eaten  by  sculpins 
and  other  predatory  fishes  before  they  are 
hatched,  and  other  thousands  of  the  defense- 
less young  fish  are  eaten  long  before  attaining 
maturity.  Of  the  great  number  produced  by 
the  parent,  a  few  only  reach  maturity  and 
produce  new  j^oung.  But  the  eggs  of  the 
robin  are  hatched  and  protected,  and  the  help- 
less fledglings  are  fed  and  cared  for  until  able 
to  cope  with  their  natural  enemies.  In  the 
next  3^ear  another  brood  is  carefully  reared,  and  so  on  for  the 
few  years  of  the  robin's  life. 

Under  normal  conditions  in  any  given  locality  the  number 
of  individuals  of  a  certain  species  of  animal  remains  about  the 
same.  The  fish  which  produces  tens  of  thousands  of  eggs 
and  the  bird  which  produces  half  a  dozen  eggs  a  year  main- 
tain equally  well  their  numbers.  In  one  case  a  few  survive 
of  many  born;  in  the  other  many  (relatively)  sm-vive  of  the  few 


Fig.  133.— Eggs 
of  lace-winged 
fly,  Chrysopa. 
The  eggs  are 
fastened  sepa- 
rately, for  pro- 
tection  from 
predaceous  in- 
sects, on  the 
tips  of  erect 
6<lender  pedi- 
cles. 


GENERATION,  SEX  AND  ONTOGENY 


227 


born;  in  hoth  cases  the  species  is  effectively  maintained.  In 
general,  no  agency  for  the  perpetuation  of  the  si)ecies  is  so 
effective  as  that  of  care  for  the  A-onng. 

Some  animals  do  not  lay  eggs,  that  is,  they  do  not  deposit 
the  fertilized  egg  cell  outside  of  the  body,  but  allow  the  develop- 
ment of  the  new  individual  to  go  on  inside  the  body  of  the 
mother  for  a  longer  or  shorter  period.  'Die  mammals  and 
some  other  animals  have  this  habit.  When  such  an  anim;'.l 
issues  from  the  body  of  the  mother,  it  is  said  to  be  born.  When 
the  developing  ani- 
mal issues  from  an 
egg  wliich  has  been 
deposited  outsitle 
the  body  of  the 
mother,  it  is  said 
to  hatch.  The  "ni- 
mal  at  birth  or  at 
time  of  hatching  is 
not  yet  fully  devel- 
oped. Only  part 
of  its  development 
or  period  of  im- 
maturity is  passed 
within  the  egg  or 
within  the  body  of 
the  motlier.  That 
part  of  its  life  thus 
passed   within  the 

egg  or  mother's  body  is  called  the  embryonic  life  or  embryonic 
stages  of  development;  while  that  j)eriod  of  development  or 
immaturity  from  the  time  of  birth  or  hatching  until  maturity 
is  reached  is  called  the  postembryonic  life  or  postembryonic 
stages  of  development. 

The  embr3^onic  development  is  from  the  beginning  uj)  to  a 
certain  point  ]:)ractically  alike,  looked  at  in  its  larger  asi)ect, 
for  all  the  many-celled  animals.  That  is,  there  are  certain 
principal  or  constant  characteristics  of  the  l)eginning  develop- 
ment w^hich  are  present  in  the  development  of  all  many-celltHl 
animals.  The  first  stage  or  j)hen()men()n  of  develoj)ment  is 
the  simple  fission  of  the  germ  cell  into  halves  (Fig.  I'Mh).  These 
two  daughter  cells  next   divide  so  that    there  are  four  cells 


Fig.  134. — First  slaves  in  the  embryonic  development  of 
the  pond  snail,  Li/innipus:  a.  Egg  cell;  b,  first  cleavage; 
c.  second  cleavage;  d,  third  cleavage;  e,  after  numerous 
cleavages;  /,  blustula — in  section;  g,  gastriila  just  form- 
ing—  in  section;  h,  gastrula  completed  —  in  section. 
(After  Rabl.) 


228  EVOLUTION  AND  ANIMAL  LIFE 

(c) ;  each  of  these  divides^  and  this  division  is  repeated  until  a 
greater  or  lesser  number  (varying  with  the  various  species  or 
groups  of  animals)  of  cells  is  produced.  These  cells  may  not 
all  be  of  the  same  size,  but  in  many  cases  they  are,  no  struc- 
turah  differentiation  whatever  being  apparent  among  them. 

The  phenomenon  of  repeated  division  of  the  germ  cell  is 
called  cleavage,  and  this  cleavage  is  the  first  stage  of  develop- 
ment in  the  case  of  all  many-celled  animals.  The  germ  or  embryo 
in  some  animals  consists  now  of  a  mass  of  few  or  many  undif- 
ferentiated primitive  cells  lying  together  and  usually  forming  a 
sphere  (Fig.  134;  c),  or  perhaps  separated  and  scattered  through 
the  food  yolk  of  the  egg.  The  next  stage  of  development  is 
this:  the  cleavage  cells  arrange  themselves  so  as  to  form  a 
usually  hollow  sphere  or  ball,  the  cells  lying  side  by  side  to 
form  the  outer  circumferential  wall  of  this  hollow  sphere  (/). 
This  is  called  the  hlastula  or  hlastoderm  stage  of  development, 
and  the  embryo  itself  is  called  the  blastula  or  blastoderm. 
This  stage  also  is  common  to  all  the  many-celled  animals. 
The  next  stage  in  embryonic  development  is  formed  by  the 
bending  inw^ard  of  a  part  of  the  blastoderm  cell  layer,  as  shown 
in  (g)  (or  the  splitting  off  inwardly  of  cells  from  a  special  part 
of  the  blastula  cell  layer).  This  bending  in  may  produce  a 
small  depression  or  groove ;  but  w^hatever  the  shape  or  extent 
of  the  sunken-in  part  of  the  blastoderm,  it  results  in  distinguish- 
ing the  blastoderm  layer  into  two  parts,  a  sunken-in  or  inner 
portion  called  the  endohlast  and  the  other  unmodified  portion 
called  the  ectohlast.  Endo-  means  within,  and  the  cells  of  the 
endoblast  often  push  so  far  into  the  original  blastoderm  cavity 
as  to  come  into  contact  with  the  cells  of  the  ectoblast  and 
thus  obliterate  this  cavity  Qi).  This  third  well-marked  stage 
in  the  embryonic  development  is  called  the  gastrida  stage,  and 
it  also  occurs  in  the  development  of  all  or  nearly  all  many- 
celled  animals. 

In  the  case  of  a  few  of  the  simple  many-celled  animals  the 
embryo  hatches — that  is,  issues  from  the  egg  at  the  time  of 
or  very  soon  after  reaching  the  gastrula  stage.  In  the  higher 
animals,  however,  development  goes  on  within  the  egg  or 
within  the  body  of  the  mother  until  the  embryo  becomes  a 
complex  body,  composed  of  many  various  tissues  and  organs. 
Almost  all  the  development  may  take  place  within  the  egg, 
so  that  when  the  young   animal    hatches  there  is  necessary 


GENERATION,   SEX    AND  ONTOGENY  220 

little  more  than  a  rapid  growth  and  increase  of  size  to  make 
it  a  fully  develoi)cd,  mature  animal.  This  is  the  case  with 
the  birds:  a  chicken  just  hatched  has  most  of  the  tissues  and 
organs  of  a  full-grown  fowl,  and  is  simi)ly  a  little  hen.  liut  in 
the  case  "of  other  animals  the  young  hatches  from  the  egg 
before  it  has  reached  such  an  advanced  stage  of  development  ; 
a  young  starfish  or  young  crab  or  young  honeybee  just  hatched 
looks  very  different  from  its  parent.  It  has  yet  a  great  dcid 
of  development  to  undergo  before  it  reaches  the  struct ur;d 
condition  of  a  fully  develo})ed  and  fully  grown  starfish  or  crab 
or  bee.  Thus  the  development  of  some  animals  is  almost 
wholly  embryonic  development — that  is,  develoi)ment  within 
the  egg  or  in  the  body  of  the  mother — while  the  development 
of  other  animals  is  largely  post  embryonic,  or  larval  develop- 
ment, as  it  is  often  called.  There  is  no  important  difference 
between  embryonic  and  postembryonic  development.  'The 
development  is  continuous  from  egg  cell  to  mature  animal, 
and  whether  inside  or  outside  of  an  egg  it  goes  on  regularly 
and  uninterruptedly. 

The  cells  which  compose  the  embryo  in  the  cleavage  stage 
and  blastoderm  stage,  and  even  in  the  gastrula  stage,  are  a|>- 
parently  all  similar;  there  is  little  or  no  differentiation  shown 
among  them.  But  from  the  gastrula  stage  on,  develoj^ment 
includes  three  important  things:  the  gradual  differentiation  f)f 
cells  into  various  kinds  to  form  the  various  kinds  of  animal 
tissues;  the  arrangement  and  grouping  of  these  cells  into  organs 
and  body  parts;  and  finally  the  developing  of  these  organs  and 
body  parts  into  the  special  condition  characteristic  of  the  species 
of  animal  to  which  the  developing  individual  belongs.  From 
the  primitive  unclifferentiated  cells  of  the  blastoderm,  develoj)- 
ment  leads  to  the  special  cell  types  of  nuiscle  tissue,  of  l)()ne 
tissue,  of  nerve  tissue;  and  from  the  generalized  condition  of 
the  embryo  in  its  early  stages,  develoj)ment  leads  to  the  s|x»cial- 
ized  condition  of  the  body  of  the  adult  animal.  l)cvelt)i)ment 
is  from  the  general  to  the  special,  as  was  said  years  ago  by 
von  Baer,  the  first  great  student  of  development. 

A  starfish,  a  beetle,  a  dove,  and  a  horse  are  all  alike  in 
their  beginning — that  is,  the  body  of  each  is  comi>osetl  of  a 
single  cell,  a  single  structural  unit.  And  they  are  all  alike,  or 
very  much  alike,  through  several  stages  of  develoi)ment ;  the 
body  of  each  is  fii'st  a  single  cell,  then  a  number  of  similar  un- 
IG 


230  EVOLUTION  AND  ANIMAL  LIFE 

differentiated  cells,  and  then  a  blastoderm  consisting  of  a  single 
layer  of  similar  undifferentiated  cells.  But  soon  in  the  course 
of  development  the  embryos  begin  to  differ,  and  as  the  3'oung 
animals  get  further  and  further  along  in  the  course  of  their 
development,  they  become  more  and  more  different  until 
each  finally  reaches  its  fully  developed  mature  form,  showing- 
all  the  great  structural  differences  -  between  the  starfish  and 
the  dove,  the  beetle  and  the  horse.  That  is,  all  animals  begin 
development  apparently  alike,  but  gradually  diverge  from  each 
other  during  the  course  of  development. 

There  are  some  extremely  interesting  and  significant  things 
about  this  divergence  to  which  attention  should  be  given. 
While  all  animals  are  apparently  alike  structurally  ^  at  the 
beginning  of  development,  so  far  as  we  can  see,  they  do  not 
all  differ  noticeably  at  the  time  of  the  first  divergence  in  de- 
velopment. The  fii'st  divergence  in  development  is  to  be 
noted  between  two  kinds  of  animals  which  belong  to  different 
great  groups  or  classes.  But  two  animals  of  different  kinds, 
both  belonging  to  some  one  great  group,  do  not  show  differences 
until  later  in  their  development.  This  can  best  be  understood 
by  an  example.  All  the  butterflies  and  beetles  and  grass- 
hoppers and  flies  belong  to  the  great  group  or  class  of  animals 
called  Insecta,  or  insects.  There  are  many  different  kinds  of 
insects,  and  these  kinds  can  be  arranged  in  subordinate  groups 
(orders),  such  as  the  Diptera,  or  flies,  the  Lepidoptera,  or  butter- 
flies and  moths,  and  so  on.  But  all  have  certain  structural 
characteristics  in  common,  so  that  they  are  comprised  in  one 
great  class — the  Insecta.  Another  great  group  of  animals  is 
known  as  the  Vertebrata,  or  backboned  animals.      The  class 


^  We  can  say  that  they  are  alike  structurally,  only  when  we  consider 
the  cell  as  the  unit  of  animal  structure.  But,  that  the  egg  cells  of  different 
animals  differ  in  their  fine  or  ultimate  structure,  seems  certain.  For  each 
one  of  these  egg  cells  is  destined  to  become  some  one  kind  of  animal,  and 
no  other;  each  is,  .indeed,  an  individual  in  simplest,  least  developed  con- 
dition of  some  one  kind  of  animal,  and  we  must  believe  that  difference  in 
kind  of  animals  depends  upon  difference  in  structure  in  the  egg  itself. 
Indeed  Wilson,  the  foremost  American  student  of  egg  structure,  believes 
himself  able  to  perceive  in  many  eggs  a  structural  differentiation  within 
the  egg  protoplasm  itself,  corresponding,  in  some  measure,  with  the  struc- 
tural differentiation  of  the  embryonic  animal  as  revealed  in  early  develop- 
mental stages. 


GENERATION,   SEX  AND  ONTOGENY  231 

Vertebrata  incliulcs  tlio  fislios,  tlic  ])atracliiaiis,  the  reptiles, 
the  birds,  and  the  maininals,  vivAx  coinposin^  a  subordinate 
group,  but  all  charactorized  l)y  the  jwssession  of  a  backbone, 
or,  more  accurately  speaking,  of  a  notochord,  a  backlKJUchkc 
structure.  Now,  an  insect  and  a  vertebrate  diverge  very 
soon  in  tlieir  develojmient  from  each  other;  but  two  insects, 
such  as  a  beetle  and  a  honeybee,  or  any  two  \('rtebrates,  such 
as  a  frog  and  a  pigeon,  do  not  diverge  from  eacli  other  so  soon. 
That  is,  all  vertebrate  iinimals  diverge  in  one  (hrection  from 
the  other  great  groups,  but  all  the  memluTs  of  the  great  group 
keep  together  for  some  time  longer.  Tlicn  the  subonhuate 
groups  of  the  Vertebrata,  such  as  the  fishes,  th(«  birds,  and  the 
others,  diverge,  and  still  later  the  different  kinds  of  animals 
in  each  of  these  groups  diverge  from  each  other. 

That  the  course  of  development  of  any  animal  from  its 
beginning  to  fully  developed  adult  form  is — in  all  its  essentials 
— fixed  and  certain  is  readily  seen.  All  rabl)its  develop  in 
the  same  way;  every  grasshopper  goes  through  the  same  de- 
velopmental changes  from  single  egg  cell  to  the  full-grown, 
active  hopper  as  every  other  grasshopper  of  the  same  kind — 
that  is,  development  takes  place  according  to  certain  natural 
laws:  the  laws  of  animal  development.  These  laws  may  !)e 
rougldy  stated  as  follows:  All  many-celled  animals  begin  life 
as  a  single  cell,  the  fertilized  egg  cell;  each  animal  goes  through 
a  certain  orderly  series  of  developmental  changes  which,  ac- 
companied by  growth,  leads  the  animal  to  change  from  single 
cell  to  the  many-celled,  com])lex  form  characteristic  of  the 
species  to  which  the  animal  l)elongs;  this  development  is  from 
simple  to  comi)lex  structural  condition;  tlie  development  is 
the  same  for  all  individuals  of  one  s])ecies.  While  all  animals 
begin  development  similarly,  the  coin-se  of  development  in 
the  different  groups  soon  diverges,  the  divergence  being  of  the 
nature  of  a  branching,  like  that  shown  in  the  growth  of  a  tree. 
In  the  free  tips  of  the  smallest  branches  we  have  represented 
the  various  species  of  animals  in  their  fully  developed  con- 
dition, all  standing  more  or  less  clearly  apart  from  each  other. 
But  in  tracing  back  the  development  of  any  kind  of  animal 
we  soon  come  to  a  point  where  it  very  much  resembles  or 
becomes  apparently  identical  with  the  development  of  some 
other  kind  of  animal,  and,  in  addition,  the  stages  j^assed  tlirougii 
in  the  developmental  course  may  very  much  resemble  the 


232 


EVOLUTION   AND  ANIMAL   LIFE 


fully  developed,  mature  stages  of  lower  animals.  To  be  sure, 
any  animal  at  any  stage  in  its  existence  differs  absolutely  from 
any  other  kind  of  animal,  in  that  it  can  develop  into  only  its 
own  kind  of  animal.  There  is  something  inherent  in  each 
developing  animal  that  gives  it  an  identity  of  its  own.  Al- 
though in  its  young  stages  it  may  be  hardly  distinguishable 
from  some  other  kind  of  animal  in  similar  stages,  it  is  sure  to 
come  out,  w^hen  fully  developed,  an  individual  of  the  same 
kind  as  its  parents  were  or  are.  A  very  3^oung  fish  and  a  very 
young  salamander  are  almost  indistinguishably  alike,  but  one 
is  sure  to  develop  into  a  fish  and  the  other  into  a  salamander. 
This  certainty  of  an  embryo  to  become  an  individual  of  a 
certain  kind  is  called  the  law  of  heredity.  Viewed  in  the  light 
of  development,  there  must  be  as  great  a  difference  between 
one  egg  and  another  as  between  one  animal  and  another,  for 
the  greater  difference  is  included  in  the  less. 

The    significance    of   the    developmental    phenomena   is    a 
matter  about  which  naturalists  have  yet  very  much  to  learn. 


Fig.  135. — Stages  in  the  development  of  the  prawn,  Peneus  potimirium:    A,  Nauplius 
larva;  B,  first  zoea  stage;  C,  second  zoea  stage.     (After  Fritz  Miiller.) 


It  is  believed,  however,  by  practically  all  naturalists  that  many 
of  the  various  stages  in  the  development  of  an  animal  cor- 
respond to  or  repeat,  in  many  fundamental  features  at  least, 
the  structural  condition  of  the  animaPs  ancestors.  Naturalists 
believe  that  all  backboned  or  vertebrate  animals  are  rclp^tcd 
to  each  other  through  being  descended  from  a  common  ancestor, 
the  first  or  oldest  backboned  animal,    In  fact,  it  is  because  all 


GENERATION,  SEX   AND   ONTOGENY 


233 


these  backboned  animals  —  the  fislies,  the  batracliians,  the 
reptiles,  the  birds,  and  the  nianinials— have  descended  from 
a  common  ancestor  that  they  all  have  u  Ijackbonc.  It  is 
beheved  that  the  descendants  of  the  first  backlmned  animal 
have  in  the  course  of  many  generations  l)ranche(l  ofT  little  by 
httle  from  the  original  type  until  there  came  to  exist  very 
real  and  obvious  differences  among  the  ]jackl)on('il  animals — 


K 


Fig.  136. — Later  stages  in  the  development  of  the  prawn,  Pcnctts  potimirium  :  D,  Mysis 

stage;  E,  adult  stage. 


differences  which  among  the  living  backboned  animals  are 
familiar  to  all  of  us.  The  course  of  develoi)ment  of  an  in- 
dividual animal  is  believed  to  be  a  very  rapid  and  evidently 
much  condensed  and  changed  recapitulation  of  the  history 
wliich  the  species  or  kind  of  animal  to  which  the  developing  in- 
dividual belongs  has  passed  through  in  the  course  of  its  descent 
through  a  long  series  of  gradually  changing  ancestors.  If  this  is 
true,  then  we  can  readilv  understand  whv  a  fish  antl  a  salaman- 
der,  a  tortoise,  a  bird  and  a  rabbit,  are  all  much  alike,  as  they 
really  are,  in  their  earlier  stages  of  development,  and  gradually 
come  to  diff(T  more  and  more  as  they  pass  through  later  and 
later  developmental  stages.     A   crab  has  a  tail   in  one  of  its 


234 


EVOLUTION  AND  ANIMAL  LWE 


developmental  stages,  so  that  at  that  time  it  looks  like  and 
really  is  like  the  mature  stage  of  some  tailed  crustacean  like 
a  crayfish.  A  barnacle,  which  looks  little  like  a  crayfish  or 
prawn  in  its  mature  stage,  is  hardly  to  be  distinguished  in  its 
immature  life  from  a  young  shrimp  or  prawn.  Sacculina,  which 
is  a  still  more  degenerate  crustacean,  is  only  a  sort  of  feeding 
sac  with  rootletlike  processes  projecting  into  the  body  of  the 
host  crab  on  which  it  lives  as  a  parasite,  but  the  young  free- 
swimming  Sacculina  is  essentially 
like  a  barnacle,  crayfish,  or  crab 
in  its  young  stage. 

However,  it  is  obvious  that 
this  recapitulation  or  repetition 
of  ancestral  stages  is  never  per- 
fect, and  it  is  often  so  obscured 
and  modified  by  interpolated 
adaptive  stages  and  characters 
that  but  little  of  an  animal's 
ancestry  can  be  learned  from  a 
scrutiny  of  its  development. 
The  fascinating  biogenetic  law 
of  Miiller  and  Haeckel  summed 
up  in  the  phrase,  "ontogeny  is 
a  recapitulation  of  phylogeny,'' 
must  not  be  too  heavily  leaned 
on  as  a  support  for  any  specula- 
tions as  to  the  phyletic  affinities  of  any  species  or  group  of 
species  of  organisms.  "  Embryology  is  an  ancient  manuscript 
with  many  of  the  sheets  lost,  others  displaced,  and  with 
spurious  passages  interpolated  by  a  later  hand.'' 

While  a  young  robin  when  it  hatches  from  the  egg  or  a 
young  kitten  at  birth  resembles  its  parents,  a  young  starfish 
or  a  young  crab  or  a  young  butterfly  when  hatched  does  not 
at  all  resemble  its  parents.  And  while  the  young  robin  after 
hatching  becomes  a  fully  grown  robin  simply  by  growing  larger 
and  undergoing  comparatively  slight  developmental  changes, 
the  young  starfish  or  young  butterfly  not  only  grows  larger, 
but  undergoes  some  very  striking  developmental  changes;  the 
body  changes  very  much  in  appearance.  Marked  changes  in 
the  body  of  an  animal  during  postembryonic  or  larval  de- 
velopment constitute  what  is  called  metamorphic  development, 


Fig.  137. — Metamorphosis  of  a  bar- 
nacle, Lepas:  a.  Larva;  b,  adult. 


GENERATION,   SEX  AND  ONTOGENY 


235 


or  the  animal  is  said  to  undergo  or  to  show  metamorphosis  m . 
its  develojnnent. 

This  metamorphosis  is  faniihar  to  all  in  insects;  to  zoologists, 
it  is  familiar  among  numerous  other  lands  of  animals.     Fi'j.  i:iS 


Fig,  138. — Metamorphosis  of  the  Monardi  ])utterny,  ,1  misia  plcxippus:    a,  IOkk;  b,  lan-a; 

c,  pupa;  (/,  imago,  or  ailult. 


shows  the  different  stages  in  the  nictaniorpliie  dcvcloiimriit 
of  the  common  hirge  red-l:)rown  milkweed  butterfly,  AfUKsia 
plexippiis.  From  the  egg  hatches  a  crawling,  wormlike  larva, 
wingless,  without  comj^ound  eyes,  and  with  strong  jaws  anil 
other  mouth  parts  fitted  for  l)iling.  This  creature  develops 
into  the  winged  butterfly  with  diiTerent  eves,  ditTerent  antenna*, 
different  mouth  parts,  different  almost  everything.  And,  by 
the  intervention  of  a  curious  (piiescent  stage  called  the  pupal 


236 


EVOLUTION  AND  ANIMAL   LIFE 


or  chrysalid  stage,  the  changes  seem  to  be  made  by  sudden 
leaps.  Of  course,  this  is  not  so.  It  is  all  done  gradually, 
although  there  are  certain  periods  in  the  course  of  the  develop- 
ment when  the  changing  is  more  rapid  and  radical  than  at 
other  times.  The  changing  is  masked  by  the  outer  covering 
of  larva  and  pupa,  and  although  it  is  indeed  startUngly  radical 
in  its  character,  it  is  wholly  continuous. 

The   metamorphosis   of  frogs   and   toads  also   is  familiar. 


^.;.:v-:..^:>."" 


:>Q^=^^^ft.. 


'^^^  '^^^^^^^^'■^V:r^-'>^^/-:^[::[.:y^^ ^^■■' 


h  -y--^ 


Fig.  139. — Stages  in  development  of  silkworm  moth. 


The  eggs  of  the  toad  are  arranged  in  long  strings  or  ribbons 
in  a  transparent  jellylike  substance.  These  jeUy  ribbons 
with  the  small,  black,  beadlike  eggs  in  them  are  wound  around 
the  stems  of  submerged  plants  or  sticks  near  the  shores  of 
the  pond.  From  each  egg  hatches  a  tiny,  wriggHng  tad- 
pole, differing  nearly  as  much  from  a  full-grown  toad  as  a 
caterpillar  differs  frc  n  a  butterfly.  The  tadpoles  feed  on  the 
microscopic  plants  to  be  found  in  the  water,  and  swim  easily 
about  by  means  of  their  long  tails.  The  very  young  tadpoles 
remain  underneath  the  surface  of  the  water  all  the  time,  breath- 
ing the  air,  which  is  mixed  with  the  Avater,  by  means  of  gills. 
But  as  they  become  older  and  larger  they  come  often  to  the 
surface  of  the  water.  Lungs  are  develoj^ing .  inside  the  body, 
and  the  tadpole  is  beginning  to  breathe  as  a  land  animal, 
although  it  still  breathes  partly  by  means  of  giii^,  that  is,  as 


GENERATION,   SEX   AND   ONTOGKN\ 


2:^7 


an  aquatic  animal.  Soon  it  is  apparent  that  altliougli  tlie 
tadj^ole  is  steadily  and  ra})idly  growinj:;  larger,  its  tail  is  grow- 
ing shorter  and  smaller  instead  of  longer  and  larger.  At  tlie 
same  time,  fore  and  hind  legs  bud  out  and  rapidly  take  form 
and  become  functional.  J^y  the  time  tliat  the  tail  gets  very 
short  indeed,  the  young  toad  is  ready  to  leave  the  water  and 
live  as  a  land  animal.  On  land  the  toad  lives,  as  we  know, 
on  insects  and  snails  and  worms.  The  metamorj)hosis  of  tlie 
toad  is  not  so  striking  as  that  of  the  butterfly,  Init  if  the  tad- 
pole were  inclosed  in  an  unchanging  opacpie  V)ody  wall  while 
it  was  losing  its  tail  and  getting  its  legs,  and  this  wall  were 
to  be  shed  after  these  changes  were  made,  would  not  the  meta- 
morphosis be  nearly  as  extraordinary  as  in  the  case  of  the 


Fig.  140.— Metamorphosis  of  the  toad:     At  left,  strings  of  crrs;  in  w.i(cr.  VBriou«   t*d- 
pole  or  larval  stages;  and  on  the  bank,  the  adult  t.mds.     (Partly  after  Cage.) 

butterfly?     But  in  the  metamori^hosis  of  the  toad  wc  can  see 
the  gradual  and  continuous  character  of  the  change. 

Many  other  animals,  besides  insects  and  frogs  and  toad.-^, 
undergo  metamorphosis.  The  just-hatched  .sea  urchin  (loes 
not  resemble  a  fully  developed  sea  urchin  at  all.     It  is  a  nnnutc 


238 


EVOLUTION  AND  ANIMAL  LIFE 


wormlike  creature,  jDrovided  with  cilia  or  vibratile  hairs,  by 
means  of  which  it  swims  freely  about.  It  changes  next  into 
a  curious  bootjack-shaped  body  called  the  pluteus  stage.  In 
the  pluteus  a  skeleton  of  lime  is  formed,  and  the  final  true  sea- 
urchin  body  begins  to  appear  inside  the  pluteus,  developing 
and  growing  by  using  up  the  body  substance  of  the  pluteus. 
Starfishes,  which   are   closely  related  to  sea  urchins,  show  a 

similar  metamorphosis, 
except  that  there  is  no 
pluteus  stage,  the  true 
starfish-shaped  body 
forming  within  and  at 
the  expense  of  the  first 
larval  stage,  the  ciliated 
free-swimming  stage. 

A  young  crab  just 
issued  from  the  egg 
(Fig.  141)  is  a  very 
different  appearing 
creature  from  the  adult 
or  fully  developed  crab. 
The  bod}^  of  the  crab 
in  its  first  larval  stage 
is  composed  of  a  short, 
globular  portion,  fur- 
nished with  conspicuous 
long  spines  and  a  rela- 
tively long,  jointed  tail. 
This  is  called  the  zoea 
stage.  The  zoea  changes  into  a  stage  called  the  megalops, 
which  has  many  characteristics  of  the  adult  crab  condition, 
but  differs  especially  from  it  in  the  possession  of  a  long,  seg- 
mented tail,  and  in  having  the  front  half  of  the  body  longer 
than  wide.  The  crab  in  the  megalops  stage  looks  very  much 
like  a  tiny  lobster  or  shrimp.  But  soon  the  bod}^  widens,  the 
tail  is  folded  underneath,  and  the  final  stage  is  reached. 

In  many  families  of  fishes  the  changes  which  take  place  in 
the  course  of  the  life  cycle  are  almost  as  great  as  in  the  case 
of  the  insect  or  the  toad.  In  the  ladyfish  (Albida  vidpes)  the 
very  young  are  ribbonlike  in  form,  with  small  heads  and  very 
loose  texture  of  the  tissues^  the  body  substance  being  jelly- 


Fig.  141. — ^Metamorphosis  of  a  crab :  a.  The  zoea 
stage;  b,  the  megalops;  c,  the  adult. 


GENERATION,   SEX   AXl)  ovTOOENY 


2:^0 


like  and  transparent.  As  the  M\  grows  okk-r  tlic  l^odv  Ix^comes 
more  compaet,  and  therefore  sliort<'r  and  thicker.  Aft<^r 
shrinking  to  the  texture  of  an  ordinary  fish,  its  growth  in  size 
begins  normally,  ahlioiigh  it  lias  all  the  time  steadily  increiiscd 
in  actual  weight.  Many  herring,  eels,  and  other  soft-lKxlicil 
fishes  pass  through  stages  similar  to  those  socn  in  the  la<lvfisli. 
Another  type  of  development  is  illustrated  in  tlie  sworilfish. 
The  young  has  a  bony  head,  bristling  witli  spines.  As  it 
grows  older  the  spines  disappear,  the  skin  grows  smoother,  and, 


a 


Fig.  142. — Three  stages  in  the  development  of  the  swordfish,  Xiphias  uladius :  a.  Very 

young;  b,  older;  c,  adult.    (After  Liitken.) 


finally,  the  bones  of  the  upper  jaw  grow  together,  forming  a 
prolonged  sword,  the  teeth  are  lost  and  the  fins  become  greatly 
modified.  Fig.  142  shows  three  of  these  stages  of  growth.  The 
flounder  or  flatfish  (Fig.  143)  when  full  grown  lies  flat  on  one 
side  when  swinnning  or  when  resting  in  the  sand  on  the  bottcHu 
of  the  sea.  The  eyes  are  both  on  the  upper  side  of  the  body, 
and  the  lower  side  is  ])\'nu\  and  colorless,  ^^'llen  the  flounder 
is  hatched  it  is  a  transparent  fish,  broad  and  flat,  swimming 
vertically  in  the  water,  with  an  eye  on  each  side.  .Vs  its  d(^ 
velopment  goes  on  it  rests  itself  ()bli(|ue]y  on  the  bottom.  \\\v 
eye  of  the  lower  side  turns  upward,  and  as  growth  procetnls  it 
passes  gradually  around  the  forehead,  its  socket  moving  with 
it,  until  both  eyes  and  sockets  are  transferred  l)y  the  twisting 


240 


EVOLUTION  AND  ANIMAL  LIFE 


of  the  skull  to  the  upper  side.  In  some  related  forms,  called 
soles,  the  small  eye  passes  through  the  head  and  not  around 
it,  appearing  finall)'  in  the  same  socket  with  the  other  eye. 

Thus  in  almost  all  the  great  groups  of  animals  we  find 
certain  kinds  which  show  metamorphosis  in  their  postem- 
bryonic  development.  But  metamorphosis  is  simply  develop- 
ment; its  striking  and  extraordinary  features  are  usually  due 
to  the  fact  that  the  orderly,  gradual  course  of  the  development 
is  revealed  to  us  only  occasionally,  with  the  result  of  giving 


Fig.  143. — Young  stages  of  a  flounder,  Platophrys  podas.     The  eyes  in   the  young 
flounder  are  arranged  normally;  that  is,  one  on  each  side  of  the  head.     (After  Emery.) 


the  impression  that  the  development  is  proceeding  by  leaps  and 
bounds  from  one  strange  stage  to  another.  If  metamorphosis 
is  carefully  studied  it  loses  its  aspect  of  marvel,  although  never 
its  great  interest. 

After  an  animal  has  completed  its  development  it  has  but 
one  thing  to  do  to  complete  its  life  cycle,  and  that  is  the  pro- 
duction of  offspring.  When  it  has  laid  eggs  or  given  birth  to 
young,  it  has  insured  the  beginning  of  a  new  life  cycle.  Does 
it  now  die?  Is  the  business  of  its  life  accomplished?  There  are 
many  animals  which  die  immediately  or  very  soon  after  laying 
eggs.  Some  of  the  May  flies — ephemeral  insects  which  issue 
as  winged  adults  from  ponds  or  lakes  in  which  they  have  spent 
from  one  to  three  years  as  aquatic  crawling  or  swimming  larvae, 
flutter  about  for  an  evening,  mate,  drop  their  packets  of  fertil- 
ized eggs  into  the  water,  and  die  before  the  sunrise — are  ex- 
treme examples  of  the  numerous  kinds  of  animals  whose  adult 
life  lasts  only  long  enough  for  mating  and  egg4aying.  But 
elephants  live  for  two  hundred  years.  Whales  probably  live 
longer.  A  horse  lives  about  thirty  years,  and  so  may  a  cat  or 
toad.  A  sea  anemone,  which  was  kept  in  an  aquarium,  lived 
sixty-six  years.  Crayfishes  may  live  twenty  years.  A  queen 
bee  was  kept  in  captivity  for  fifteen  years.     Most  birds  have 


GENERATION,   SEX   AND   OXTOOKXY  2U 

long  lives — the  small  sonjz;  l)ir(l.s  from  oi^^lit  to  ci^litccn  years, 
and  the  great  eagles  and  vultures  u{)  to  a  liundred  years  or 
more.  On  the  other  hand,  among  all  tlie  thousands  of  species 
of  insects,  tlie  individuals  of  very  few  indeed  hve  more  than  a 
year;  the  adult  life  of  most  insects  being  l)ut  a  few  days  or  weeks, 
or  at  best  months.  Even  among  tlie  higher  animals,  some  are 
very  short-lived.  In  Japan  is  a  small  fish  (Sahnix)  which  prob- 
ably lives  but  a  year,  ascending  the  rivers  in  numbers  when 
young  in  the  spring,  the  whole  mass  of  individuals  dying  in  the 
fall  after  spawning. 

Naturalists  have  sought  to  discover  the  reason  for  the.se 
extraordinary  differences  in  the  duration  of  life  of  different 
animals,  and  while  it  cannot  be  said  that  the  reason  or  reasons 
are  wholly  known,  yet  the  probability  is  strong  that  the  dura- 
tion of  hfe  is  closely  connected  with,  or  dejx'ndent  upon,  the 
conditions  attending  the  production  of  offs})ring.  It  is  not 
sufficient  that  an  adult  animal  shall  i)roduce  simj:)ly  a  single 
new"  individual  of  its  kind,  or  even  only  a  few.  It  must  })roduce 
many,  or  if  it  produces  comparatively  few  it  nnist  devote  great 
care  to  the  rearing  of  these  few,  if  the  perpetuation  of  the 
species  is  to  be  insured.  Now,  almost  all  long-livcnl  animals 
are  species  which  produce  but  few  offspring  at  a  time,  and 
reproduce  only  at  long  intervals,  wliile  most  short-lived  animals 
produce  a  great  many  eggs,  and  these  all  at  one  time.  I>irds 
are  long-lived  animals;  as  we  know,  most  of  them  lay  eggs  but 
once  a  year,  and  lay  only  a  few  eggs  each  time.  Many  of  the 
sea  birds  which  swarm  in  countless  numbers  on  the  rocky 
ocean  islets  and  great  sea  cliffs  lay  only  a  single  egg  once  each 
year.  And  these  birds,  the  guillemots  and  nmrres  and  auks, 
are  especially  long-lived.  Insects,  on  the  contrary,  usually 
produce  many  eggs,  and  all  of  them  in  a  short  time.  The  May 
fly,  with  its  one  evening's  lifetime,  lets  fall  from  its  body  two 
packets  of  eggs  and  then  dies.  Thus  the  shortening  of  the 
period  of  reproduction  with  the  production  of  a  great  many 
offspring  seem  to  be  always  associated  with  a  short  adult  life- 
time; while  a  long  period  of  reproduction  with  the  production 
of  few  offspring  at  a  time  and  care  of  the  offspring  are  as,so- 
ciated  with  a  long  adult  lifetime. 

At  the  end  comes  death.  After  the  animal  has  completed 
its  Hfe  cycle,  after  it  has  done  its  share  toward  insuring  the 
perpetuation  of  its  species,  it  dies.    It  may  meet  a  violent 


242  EVOLUTION  AND  ANIMAL  LIFE 

death,  may  be  killed  by  accident  or  by  enemies,  before  the  life 
cycle  is  completed.  And  this  is  the  fate  of  the  vast  majority 
of  animals  which  are  born  or  hatched.  Or  death  may  come 
before  the  time  for  birth  or  hatching.  Of  the  millions  of  eggs 
laid  by  a  fish,  each  egg  a  new  fish  in  simplest  stage  of  develop- 
ment, how  many  or  rather  how  few  come  to  maturity,  how 
few  complete  the  cycle  of  life! 

Of  death  we  know  the  essential  meaning.  Life  ceases 
and  can  never  be  renewed  in  the  body  of  the  dead  animal.  It 
is  important  that  we  include  the  words  "  can  never  be  renewed, ^^ 
for  to  say  simply  that  ''life  ceases, ^^  that  is,  that  the  perform- 
ance of  the  life  processes  or  functions  ceases,  is  not  really  death. 
It  is  easy  to  distinguish  in  most  cases  between  life  and  death, 
between  a  live  animal  and  a  dead  one,  yet  there  are  cases  of 
apparent  death  or  a  semblance  of  death  which  are  very  puzzling. 
The  test  of  life  is  usually  taken  to  be  the  performance  of  life 
functions,  the  assimilation  of  food  and  excretion  of  waste,  the 
breathing  in  of  oxvgen,  and  breathing  out  of  carbonic-acid 
gas,  movement,  feeling,  etc.  But  some  animals  can  actually 
suspend  all  of  these  functions,  or  at  least  reduce  them  to  such 
a  minimum  that  they  cannot  be  perceived  by  the  strictest  exam- 
ination, and  yet  not  be  dead ;  that  is,  they  can  renew  again  the 
performance  of  the  life  processes.  Bears  and  some  other 
animals,  among  them  many  insects,  spend  the  winter  in  a  state 
of  deathlike  sleep.  Perhaps  it  is  but  sleep;  and  yet  hibernat- 
ing insects  can  be  frozen  solid  and  remain  frozen  for  w^eeks  and 
months,  and  still  retain  the  power  of  actively  living  again  in 
the  following  spring.  Even  more  remarkable  is  the  case  of 
certain  minute  animals  called  Rotatoria  and  of  others  called 
Tardigrada,  or  bear  animalcules.  These  bear  animalcules  live 
in  water.  If  the  water  dries  up,  the  animalcules  dry  up  too ; 
they  shrivel  into  formless  little  masses  and  become  desiccated. 
They  are  thus  simply  dried-up  bits  of  organic  matter;  they  are 
organic  dust.  Now,  if  after  a  long  time — years  even — one  of 
these  organic  dust  particles,  one  of  these  dried-up  bear  ani- 
malcules, is  put  into  water,  a  strange  thing  happens.  The  body 
swells  and  stretches  out,  the  skin  becomes  smooth  instead  of 
all  wrinkled  and  folded,  and  the  legs  appear  in  normal  shape. 
The  body  is  again  as  it  was  years  before,  and  after  a  quarter 
of  an  hour  to  several  hours  (depending  on  the  length  of  time 
the  animal  has  lain  dormant  and  dried)  slow  movements  of 


GENERATION,  SEX  AXI)  OXTOCKXV       243 

the  body  parts  begin,  cand  soon  the  animak'nle  orawls  about, 
begins  again  its  hfe  where  it  had  been  interruptccl.  \'arious 
other  small  animals,  such  as  vinegar  eels  and  certain  Protozoa, 
show  similar  powers.  Certainly  here  is  an  interesting  problem 
in  life  and  death. 

When  death  comes  to  one  of  the  animals  with  wiiich  we 
are  familiar,  we  are  accustomed  to  think  of  its  coming  to  the 
whole  body  at  some  exact  moment  of  time.  As  we  stand 
beside  a  pet  which  has  been  fatally  injured,  we  wait  mitil 
suddenly  we  say,  "  It  is  dead  ! "  As  a  matter  of  fact,  it  is  diffi- 
cult to  say  when  death  occurs.  Long  af1(>r  the  heart  cea.ses 
to  beat,  other  organs  of  the  body  are  alive — that  is,  are  able  to 
perform  their  special  functions.  The  muscles  can  contract  for 
minutes  or  hours  (for  a  short  time  in  warm-blooded,  for  a  long 
time  in  cold-blooded  animals)  after  the  animal  ceases  to  breathe 
and  its  heart  to  beat.  Even  longer  live  certain  cells  of  the 
body,  especially  the  amoel^oid  white  blood  corpuscles.  The.se 
cells,  much  like  the  Amoeba  in  character,  live  for  days  after  the 
animal  is,  as  we  say,  dead.  The  cells  which  hne  the  tracheal 
tube  leading  to  the  lungs  bear  cilia  or  fine  hairs  which  they 
wave  back  and  forth.  They  continue  this  movement  for  days 
after  the  heart  has  ceased  beating.  Among  cold-blooded  ani- 
mals, hke  snakes  and  turtles,  complete  cessation  of  life  -func- 
tions comes  very  slowly,  even  after  the  body  has  been  literally 
cut  to  pieces. 

Thus  it  is  essential  in  defining  death  to  speak  of  a  complete 
and  permanent  cessation  of  the  performance  of  the  life  processes. 

/ 


CHAPTER  XIII 

FACTORS  IN   ONTOGENY  AND  EXPERIMENTAL 

DEVELOPMENT 

Many  biologists  find  their  greatest  triumph  in  the  doctrine  that  the 
living  body  is  a  "mere  machine/'  but  a  machine  is  a  collocation  of 
matter  and  energy  working  for  an  end,  not  a  spinning  toy,  and  when 
the  n\'ing  machine  is  compared  to  the  products  of  human  art  the 
legitimate  deduction  is  that  it  is  not  merely  a  spinning  eddy  in  a 
stream  of  dead  matter  and  mechanical  energy,  but  a  little  garden  in 
the  physical  wilderness. 

What  the  distinction  (between  vital  and  nonvital)  may  mean  in 
ultimate  analysis,  I  know  no  more  than  Aristotle  or  Huxley,  nor  do 
I  believe  that  anyone  will  know  until  we  find  out. — Brooks. 

While  in  the  foregoing  chapter  there  is  outlined  in  some 
detail  the  general  facts  and  processes  and  so-called  "laws''  of 
ontogenetic  development,  ^ve  purposely  omitted  any  reference 
to  what  is  known  or  guessed  concerning  the  causes  and  control 
of  this  development.  Only  less  wonderful  than  life  itself  is 
the  unfolding  and  changing  of  a  single  tiny  apparently  homo- 
geneous speck  of  life  substance  (a  fertilized  egg  cell),  into  a 
great  myriad-celled,  extraordinarily  heterogeneous,  but  per- 
fectly organized  fully  developed  plant  or  animal  body.  And 
only  second  in  point  of  insistence  to  man's  queries  about  the 
Avhence  and  whither  of  life  itself  are  his  demands  to  be  informed 
concerning  the  causes  and  control  of  development.  It  is  indeed 
strongly  felt  by  most  biologists  that  the  study  of  development, 
that  is,  the  study  of  the  initiating  and  guiding  factors  of  de- 
velopment, is  more  likely  to  reveal  to  us  the  basic  factors  and 
mechanism  of  evolution  than  any  other  kind  of  study.  It  is 
plain  that  evolution,  its  causes  and  method,  are  intimately 
bound   up   with  the  general   primary   phenomena   of  life,  as 

244 


FACTORS  IX   OXTOGEXY  245 

assimilation,  growth,  difforontiation,  adaptation,  hrrodity, 
variation,  etc.,  and  it  is  also  ])lain  tliat  those  fuiKhunontal  life 
phenomena  are  to  be  most  effectively  studied  in  their  relations 
to  the  development  of  individual  organisms. 

The  most  casual  analysis  of  development  shows  tliat  nu- 
merous and  various  influences  ])lay  their  parts  in  determining 
its  course;  it  satisfies  no  one  any  longer  to  say  that  the  course 
and  character  of  an  animal's  development  is  determined  by 
heredity.  No  influence  or  "force''  of  lieredity  can  make  up 
in  any  degree  in  the  case  of  the  development  of  a  chick,  for 
example,  for  the  absence  of  a  proper  temperature.  This  ])ur('ly 
external  factor  of  heat  is  as  indispensable  to  the  development  of 
the  new  chick  creature  as  is  the  mysterious  inherent  capacity  of 
the  tiny  protoplasmic  mass  to  unfold  or  change  so  radically 
tliat  it  (and  what  it  adds  to  itself)  may  become  a  ])eeping 
chicken.  And  temperature  is  but  one  of  a  numix'r  of  other 
external  factors  that  contribvte  to  the  creation  of  the  new 
chicken,  as  indeed  the  inherent  capacity  of  the  protoj)lasm 
of  a  hen's  egg  cell  to  rearrange  itself  chickwise  and  no  other 
wise  during  development  is  but  one  among  a  number  of  neces- 
sary intrinsic  factors  whose  correlated  influence  or  working  is 
part  of  the  developmental  mechanism. 

The  influences  or  factors  which  determine  the  initiation, 
course,  and  outcome  of  development,  then,  may  be  roughly 
classified  into  intrinsic  and  extrinsic  factors.  Antl  as  in  our 
search  for  rational  mechanical  explanations  of  vital  ])henonien:i 
we  look  on  factors  as  causal,  we  mav  use  the  word  ''causes" 
in  place  of  "factors"  or  "influences"  if  we  Hke.  The  intrinsic 
causes  we  must  believe  to  be  dependent  on  or  incident  to  the 
protoplasmic  structure  of  the  germ  stuff  and  to  be  largely  the 
guiding  and  determining  factors  in  development,  while  the 
extrinsic  causes  are  largely  such  as  supply  stimulus  and  energy 
for  the  development.  Among  intrinsic  developmental  factors 
are  included  assimilation,  growth,  division,  ditTerentiation. 
etc.,  all  constituting  what  His  calls  the  "law  of  growth  ";  under 
extrinsic  factors  may  be  listed  heat,  light,  moisture,  food, 
gravitation,  osmosis,  etc.,  composing,  according  to  His,  the 
conditions  under  which  the  "law  of  growth"  operates. 

In  order  to  understand  just  what  part  each  one  of  the  vari- 
ous developmental  factors  or  causes  jilays,  there  is  necessary 
a  most  thorough  analytical  study  of  development,  and  an 
17 


246  EVOLUTION  AND  ANIIklAL  LIFE 

attempt  o  determine  in  measurable  or  quantitative  degree  just 
what  specific  effects  each  factor  produces.  Obviously  the  most 
reliable  way  to  effect  this  analysis  and  this  determination  of 
the  specific  cause  and  effect  relations  is  to  appeal  to  experi- 
ment. But  biology  has  always  been  looked  on  as,  and  until 
recently  has  actually  been,  almost  wholly  a  science  of  observa- 
tion. It  is  now  becoming,  in  part  at  least,  a  science  of  experi- 
ment as  chemistry  and  physics  have  long  been  (these  are  now 
becoming  more  and  more  sciences  of  calculation,  that  is,  exact 
sciences  like  mathematics),  and  this  change  and  advance — for 
it  is  truly  an  advance  when  a  science  formerly  relying  for  its 
facts  on  observation  begins  to  base  its  foundations  on  the 
results  of  experiment — is  due  primarih^  to  the  modern  interest 
and  work  in  the  problem  of  developmental  causes.  The  search 
for  a  rational,  causomechanical  explanation  of  the  complex 
and  at  first  sight  wholly  baffling  phenomena  of  development 
has  been  a  great  stimulus  to  the  bold  questioning  of  many 
other  vital  phenomena  heretofore  looked  on  as  to  be  explained 
only  by  the  assumption  of  a  mystic  vital  force  or  capacity 
wholly  beyond  and  foreign  to  the  physicochemical  world  of 
matter  and  force.  Mechanism  versus  vitalism  is  one  of  the 
greatest  present-day  battles  in  biology,  and  nowhere  is  the 
straggle  keener  or  are  the  mechanists  more  bold  in  their  posi- 
tion than  in  the  particular  field  of  the  processes  and  factors  of 
development.  To  the  mechanists  the  play  of  familiar  physico- 
chemical  forces  through  the  complex  and  unique  structure  of 
germ  plasm  and  living  tissues  has  for  result  all  the  extraor- 
dinary outcome  of  developmental  course  and  outcome;  to  the 
vitalists  this  coiu-se  and  outcome  are  far  too  complex  and  pur- 
poseful to  be  explicable  without  the  assumption  of  an  extra- 
physicochemical  force,  wiih.  a  capacity  beyond  any  single  or 
any  combination  of  several  physicochemical  forces,  which 
they  call  vitalism. 

There  is  little  need  of  discussing  the  great  mechanism 
versus  vitalism  problem  here:  it  is  too  difficult  a  subject,  and 
one  as  yet  too  little  illuminated  by  known  facts,  to  introduce 
into  any  elementary  discussion  of  evolution  matters.  But 
it  may  not  be  amiss  to  call  the  attention  of  even  the  most 
elementary  student  of  evolution  and  general  bionomics  phenom- 
ena to  the  obvious  fact,  that  the  moment  one  indulges  a 
penchant  for  assuming  a  mystic,  extra-physicochemical  force 


FACTORS   IN    OXTOdKNY  247 

to  explain  a  particularly  hard  prol^lom;  one  lias  siniplv  reniov<'<l 
his  problem  from  the  realm  of  scientific  investigation.  It  is 
no  longer  a  problem.  It  is  explained— that  is,  it  is  explained 
for  whoever  accepts  the  vitalistic  assum])tion. 

The  varying  behavior  of  things  in  the  inorganic  world,  tlie 
functions  and  ca])acities  of  these  things,  dej)en(l  on  tlu^  varying 
physical  and  chemical  make-u])  of  these  things  acted  upon  \)y 
the  various  kinds  of  energy,  such  as  heat,  motion,  electricity, 
and  what  not,  which  we  are  more  or  less  familiar  witli  as  a  ])art 
of  the  physicochemical  world,  ^'arying  energy  acting  upon, 
or  better,  through  varying  structure:  this  is  the  causomechanical 
explanation  of  all  the  phenomena  in  the  inorganic  world. 
Should  we  not  in  any  o])en-minded  consideration  of  the  phe- 
nomena in  the  organic  world  strongly  incline  to  hc)l(l  to  this 
same  explanation  until  it  is  definitely  ])roved  incomi)etent. 
untenable?  Answering  the  question  with  a  hearty  "Yes," 
the  mechanists  look  first  of  all  in  their  study  and  analysis  of 
the  so-called  vital  phenomena  to  the  matter  of  structure  o( 
the  vital  masses  and  to  the  play  of  energy  through  the  masses, 
to  discover,  if  possible,  a  tangible  clew  to  the  "mysteries"  of 
the  life  process.  In  the  study  of  development,  then,  we  strive 
first  to  see  and  to  understand  the  intimate  structure  of  the 
germ  plasm,  this  protoplasmic  stuff  with  its  wondrous  endow- 
ment of  potentiality. 

In  Chapter  III  we  have  already  stated  sunnnarily  what  is 
known  of  the  chemical  and  j)hysical  make-up  of  protoplasm. 
What  is  actually  known,  by  chemical  analysis  and  earn(*st 
microscopic  peering,  of  this  structural  make-u})  is  wholly  in- 
sufficient to  serve  as  a  satisfactory  basis  of  any  causomechani- 
cal explanation  of  protoplasmic  ])roperties.  Although  some 
of  the  simpler  capacities  of  protoi)lasm.  as  its  motion,  its 
taking  up  of  outside  substances  (feeding),  etc..  have  been  to 
some  degree  explained  by  seeing  in  them  direct  physicochem- 
ical reactions  to  external  stinnili  or  conditions,  practically 
nothing  has  been  really  acc()m})lished  as  yet  toward  a  mecliani- 
cal  explanation  of  such  more  comi)lex  or  unusual  cai)acities 
as  irritabiUty,,  assimilation,  and  reproduction.  This  last  func- 
tion of  protoplasm  is  in  a  way  its  most  ai)parently  hope- 
lessly inexplicable  property.  And  this  is  esi)ecially  so  when 
the  reproduction  is  of  the  sort  peculiar  to  the  germinal  proto- 
plasm; that  is,  where  the  reproducing  protoplasmic  mass  doe.*^ 


248 


EVOLUTION   AND   ANIMAL   LIFE 


X>V^<:)-  >-C:V-.>.;r>  V<vv?>  /-.. 


>  •■■•  >-.— I.  :■■..«■- 


not  simply  divide  and  t^us  make  two  masses  each  capable  of 
the  growth  and  change  necessary  to  make  it  like  the  parent 
mass,  but  where  the  parent  mass  (a  fertilized  egg  cell,  or  a  sexual 
egg  or  bud  cell)  can  grow  and  develop  into  a  highly  complex 
many-celled  new  organism  of  type  like  that  from  which  the 
parent  germ  plasm  was  derived.  The  special  capacities,  there- 
fore, of  germ  plasm  have  furnished  for  centuries,  and  do  to-day, 

the  great  problem  of  biology 
(next  to  that  provided  by  the 
existence  of  life  itself). 

If  we  cling  to  a  belief  that 
in  some  way,  after  all,  the  ex- 
planation of  the  general  proto- 
plasmic and  special  germ  plasm 
capacities  lies  in  an  unusual 
combination  of  structure  and 
play  of  familiar  form  of  energy 
through  the  structure,  we  arc 
at  once  forced  to  assume  a 
structural  make-up  of  proto- 
plasm and  germ  plasm  beyond 
the  highest  powers  of  our  mi- 
croscopes to  detect.  And  this 
assumption  actually  is  made 
by  most  biologists.  No  agree- 
ment, however,  exists  among  biologists  as  to  this  assumed 
structure.  Biology  does  not  have  its  atomic  theory  as  chemistry 
does,  to  explain  the  ultramicroscopic  make-up  of  the  sub- 
stances with  which  it  has  to  deal,  but  has  its  atomic  theories, 
a  score  of  fairly  well-marked  theories  as  to  the  ultimate  struc- 
ture of  germ  plasm  having  been  advanced  in  the  last  couple  of 
centuries  of  biologic  study. 

Almost  all  of  these  theories  assume  a  micromeric  structure 
of  protoplasm;  a  few  are  antimicromeric.  By  mjcromerio  is 
meant  simply  that  the  plasm  which  appears  to  us  as  a  viscous 
colloidal  substance,  somewhat  differentiated  into  denser  and 
less  dense  parts,  appearing  as  fibrils  or  grains  or  alveoles  in  a 
ground  substance  of  different  density,  is  assumed  to  be  com- 
posed of  myriads  of  minute,  ultramicroscopic  units  of  the 
general  nature  of  combinations  of  chemical  molecules.  These 
unit  combinations  are  given^  in  the  theories  of  various  authors, 


Fig.  144. — Egg  cell  of  a  sea  urchin,  Toxo- 
pneustes  lividus,  showing  cytoplasm, 
nucleus,  and  nucleolus,  and  network 
or  alveolar  appearance  of  the  proto- 
plasm.    (After  Wilson.) 


FACTORS   IN   ONTOGENY  240 

various   names,   endowed    with    various   particular   prop(»rties, 
and  attributed,  as  to  their  origin,  to  varying  sources. 

In  the  seventeenth  century  and  early  part  of  the  eigliteonth 
century,  before  the  time  of  the  microscope,  many  naturalists 
and  physicians  believed  that  in  each  germ  cell  (or,  according  to 
some,  in  each  egg  cell,  according  to  others,  in  each  sperm  cell) 
there  existed,  preformed  and  almost  comj)lete,  a  new  organism 
in  miniature,  and  that  development  was  simj)ly  the  expanding 
and  growing  up  of  this  tiny  embryo  man,  or  monkey,  or  chick. 
Also  they  were  forced  to  believe,  if  this  first  assumption  were 
true,  that  in  each  preformed  em])ryo  still  smaller  replicas  of 
their  particular  kind  must  exist  to  be  the  children  of  this  child, 
and  so  on,  ad  infinitum.  Like  the  nests  of  Japanese  boxes,  the 
outer  one  encasing  a  smaller  and  this  still  a  smaller,  and  this 
yet  a  smaller  and  so  on,  the  young  and  future  yoijng  of  any 
kind  of  organism  were,,  according  to  this  encasement  theory 
of  the  germ  cell  structure,  nested  in  the  egg  and  sperm  cells  of 
any  organism. 

But  the  invention  and  use  of  the  microscope  soon  put  this 
theory  aside.  The  germ  cells  were  foimd  to  contain  no  j^re- 
formed  embryo.  Indeed,  they  seemed  to  the  earlier  micro- 
scopists  to  be  utterly  homogeneous  Uttle  specks  or  masses  of 
protoplasm,  and  the  pendulum  of  speculative  explanation 
tended  to  swing  well  away  from  any  preformation  theory 
toward  the  speedily  formulated  epigenetic  theories,  which 
assumed  that  all  germ  cells  were  practically  alike  except  as 
to  their  paternity  and  maternity,  and  that  the  development  of 
these  homogeneous  specks  of  protoplasm  must  be  determined 
chiefly  by  external  conditions  and  influences. 

However,  it  was  obvious  that  there  was  no  logical  or 
even  fair  reason  for  believing  that  the  lack  of  structural 
differentiation  in  the  germ  plasm  revealed  by  the  micro- 
scope was  a  proof  of  the  actual  absence  of  such  organiza- 
tion. The  first  microscope  magnified  but  a  few  hundred 
diameters,  revealing  structure  invisible  to  the  unaided  eye; 
but  later  microscopes,  magnifying  {)l)jects  a  thousand  and 
more  diameters,  revealed  structure  and  organization  which 
w^ere  quite  invisil^le  to  the  lower-powered  instruments.  And 
so,  although  to-day  we  examine  germ  plasm  witli  lenses 
magnifying  three  thousand  times,  and  yet  fail  to  discover 
more    than    threads,   rods,   grains,   or    droplets    in    a    viscous 


250  EVOLUTION  AND  ANIMAL  LIFE 

ground  substance,  we  do  not  believe  at  all  that  this  struc- 
tural differentiation  is  the  ultimate  physical  make-up  of  the 
mysterious  substance  protoplasm.  We  readily  believe  there 
may  exist  an  ultramicroscopic  structure  of  great  complexity. 

Buffon  suggested  that  the  living  stuff  is  composed  ultimatsly 
of  tiny  structural  units,  which  he  called  organic  molecules  ] 
these  molecules  are  universal  and  indestructible;  they  do  not 
increase  in  number  or  decrease;  when  united  in  groups  they 
form  organisms;  when  an  organism  dies  its  organic  molecules 
are  freed  but  not  destroyed,  and  later  may  help  compose  o^her 
organisms.  Bechamp  believed  in  similar  living  micromeric 
units  called  microzyrnes ,  created  directly  by  the  Supreme  Being, 
indestructible  and  strewed  everywhere  in  earth,  air,  and  water. 

Herbert  Spencer  postulated  the  existence  of  so-called  phys- 
iological units:  living  units  all  of  the  same  structure,  active 
because  of  their  polarity  of  form  and  of  molecular  vibrations, 
in  size  and  character  midway  between  molecules  and  cells, 
small  but  complex  and  possessed  of  a  delicate  and  precise 
polarity  analogous  to  that  of  the  molecules  of  crystalline  sub- 
stances, a  polarity  w^hich  gives  them  the  capacity  to  group 
themselves  into  organic  parts  and  wholes.  Other  theories 
similar  to  Spencer's  assume  a  special  physicochemical  en- 
dowment of  the  chemical  molecules  in  the  organic  body  (Ber- 
thold),  or  a  special  electrical  endowment  of  the  life  units  (Fol), 
or  a  special  chemical  one  (Altmann  and  Maggi),  or,  finally,  a 
special  vital  one  (Wiesner). 

Darwin  proposed  a  theory  to  explain  how  the  germ  plasm 
could  unfold  into  the  whole  body,  called  the  theory  of  the 
pangenesis  of  gemmules.  Darwin  postulated  the  existence  in 
the  body  of  a  host  of  life  units  called  gemmules  to  be  found 
in  all  the  various  body  cells,  capable  of  rapid  self-multiplica- 
tion and  of  a  migratory  movement  through  the  body,  the  direc- 
tion and  goal  of  which  movement  is  determined  by  delicate 
afl^nities  existing  among  the  various  gemmules.  When  a  gem- 
mule  enters  an  undifferentiated  or  developing  cell,  as  yet 
gemmuleless,  it  controls  the  development  of  that  cell.  Thanks 
to  the  dehcate  and  precise  affinities  of  the  gemmules,  they 
always  get  to  just  where  they  should,  to  produce  harmonious 
development;  but  in  the  germ  cells  lodge  gemmules  from  all 
over  the  body,  so  the  development  of  these  cells  results  in  a 
new  whole  body. 


FACTORS   IX    ()\T()(ii:NV  2")! 

Nageli,  a  philoso})hic;il  Ijohinist.  proposed  ii  tlioory  of  ponn- 
plasm  stnictiire  and  ])eliavior  Avliicli  iiiav  \)v  called  the  theory 
of  micellw,  nutritive  plasm  and  idioptdsni.  When  the  complex, 
life-charaotcrizin<:;  all)uininous  sul)shin('es  took  their  l)irth  in  an 
aqueous  li(iuid,  they  were  ])recipitat(Ml  jis  tiny  particles  callcfl 
micella',  which  attracted  other  micella'  to  themselves  and  thus 
produced  aggregates  of  primitive  life  MwH.  or  protoplasm.  The 
micelLT  are  all  separated  from  each  other  by  thin  enveloiK's 
of  water,  thus  making  water  an  integral  part  of  j)roloplasm, 
and  making  growth  by  intercalation  of  new  micelhe  possible; 
this  primitive  protoi)lasm  becomes  arnvnged  in  two  ways, 
resulting  in- producing  two  kinds,  one  called  nutritive  proto- 
plasm, and  the  other  idio})lasm  or  germ  ])lasm,  extending  all 
through  the  nutritive  protoplasm  as  a  fine  network. 

Finally,  the  most  recent  micromeric  theory  of  germ-plasm 
structure  is  that  of  Weismann,  the  modern  champion  of  natural 
selection.  According  to  him  the  protoi)lasm  of  the  nucleus  is 
made  up  of  imits  called  hiophors,  which  are  the  bearers  of  the 
individual  characters  of  the  cell;  the  biophors  are  com|)lex 
groups  of  molecules,  capable  of  assimilating  food,  growing, 
and  reproducing;  the  number  of  biophors  is  enormous,  as  it 
must  ecjual  the  possibilities  of  cell  variety.  The  bi<)i)hors  are 
united  into  fixed  groups  called  determinants,  each  determinant 
containing  all  the  biophors  necessary  to  determine  the  whole 
character  of  any  one  cell;  in  each  specialized  cell  there  need 
be  but  one  determinant,  but  in  the  germ  cells  every  kind  of 
determinant  must  be  represented. 

In  connection  with  the  postulation  concerning  the  ultimate 
make-up  of  the  plasm  of  the  germ  cell,  Weismann  has  fornui- 
lated  a  theory  of  germinal  selection  to  account  for  the  obvious 
fact  that  a  certain  cumulation  of  variation  of  a  certain  kind  or 
along  fixed  lines  may  take  i)lace  without  the  aid  of  natural 
selection:  this  variation  cunuilation  often  being  intleed  of  a 
degree  too  slight  to  give  any  oi)portunity  for  interference  by 
natural  selection.  To  account  for  this  fact,  which  has  been 
much  used  by  adverse  critics  of  natural  selection.  Weismann 
assumes  a  competition  of  the  determinants  in  the  germ  cells 
for  food,  hence  for  opportunity  to  grow,  to  be  vigorous,  and  to 
multiply;  the  initially  slightly  stronger  or  more  favorably 
situated  determinants  will  get  the  most  food,  lessening,  at  the 
same  time,  the  food  supply  of  others.     Now,  when  the  germ  cell 


252  EVOLUTION   AND  ANIMAL   LIFE 

begins  development  the  kind  of  cells  or  tissues  or  organs  will 
be  best  developed  whose  determinants  happen  to  be  the  better 
fed,  stronger  ones,  while  other  parts  of  the  body  may  be  made 
smaller  or  even  not  appear  at  all  on  account  of  the  starvation 
of  their  determinants;  also  the  stronger  determinants  in  the 
better  developed  parts  of  the  body  will  produce  by  multiplica- 
tion more  and  stronger  daughter  determinants  for  the  germ 
cells  of  the  new  individual  than  the  weak  determinants  in  the 
ill-developed  body  parts,  and  thus  this  disparity  in  develop- 
ment of  body  parts  will  be  passed  on,  cumulatively,  to^  suc- 
cessive generations :  which  is  nothing  more  nor  less  than .  de- 
terminate variation. 

All  the  speculations  about  the  ultimate  structure  of  the 
germ  plasm  are  interesting,  but  none  of  them  of  course  is  really 
convincing.  As  Delage  has  well  said,  the  chances  are  too  many 
to  one  against  the  probability  of  anyone's  guessing  correctly 
the  actual  facts  concerning  the  complex  structural  detail  of 
the  protoplasmic  make-up.  The  structural  or  inherent  factors 
in  ontogeny,  then,  are  to  be  understood  only  in  so  far  as  ob- 
vious results  or  effects  may  reveal  them.  Now  there  is  one  set 
of  phenomena  in  ontogem^,  to  which  we  have  not  as  yet  called 
attention,  which  does  seem  to  throw  some  light  on  certain 
essential  features  or  facts  of  germ-cell  structure  which  other- 
wise would  not  be  obvious  to  us.  This  set  of  phenomena  is 
that  called  mitosis  or  karyokinesis ,  and  occurs  in  connection 
with  each  division  or  cleavage  of  the  egg  cells,  and  of  their 
daughter  cells  or  blastomeres.  It  occurs  also  in  the  division 
or  multiplication  of  cells  in  all  the  tissues  of  the  body,  and  is 
a  phenomenon  normal  to  cell  increase  anywhere  in  the  body 
at  any  time  in  the  life  of  the  organism. 

Direct  or  amitotic  cell  division  is  much  less  common  and 
seems  to  be  restricted  to  certain  kinds  of  tissues  or  to  certain 
periods  in  the  history  of  the  life  of  certain  tissues.  However, 
the  recent  investigations  of  Child  and  others  show  that  cell  di- 
vision without  mitosis  is  more  common  than  is  usually  thought. 
In  this  kind  of  division,  the  process  consists  simply  of  the  con- 
striction and  equal  (or  unequal)  splitting  of  the  cell  body  into 
two  parts,  the  dividing  of  the  nucleus  usually  being  slightly 
in  advance  of  that  of  the  cytoplasm.  Each  half  of  the  parent 
cell  has  then  but  to  increase  in  size  to  become  the  counterpart 
gf  its  progenitor,    In  the  mitotic  or  indirect  division,  on  the 


FACTORS   IN   OXTOGENY  253 

contrary,  the  process  is  more  complex.     It  has  been  described 
by  F.  M.  McFarland  ^  as  follows: 

"One  of  the  earliest  results  of  the  study  of  cell  mult iplirat ion  was 
the  discovery  that  division  of  the  nucleus  precedes  the  division  of  tlie 
cell  body.  Furthermore,  a  careful  examination  of  the  different  ]>ha,ses 
of  the  process  offers  the  strongest  proof  that  the  most  important 
feature  of  this  division,  an  end  to  which  all  the  other  proce.sses  are 
subsidiary,  is  the  exact  halving  of  a  certain  nuclear  substance,  the 
chromatin,  between  the  two  daughter  cells  which  result  from  tlie 
division.  To  gain  a  clear  conception  of  tliis  process  of  indirect  cell 
division,  called  'mitosis'  or  'karyokinesis,'  let  us  consider  the  clianges 
which  take  place  in  typical  cell  mult ii)licat ion.  Two  parallel  series 
of  changes  occur  nearly  simultaneously,  the  one  affecting  the  nucleus, 
the  other  the  cytoplasm.  In  the  so-callctl  'resting'  nucleus — i.  e., 
the  nucleus  not  in  active  division — the  chromatin,  as  we  have  seen, 
exists  usually  in  the  form  of  scattered  granules  arranged  along  the 
linin  network,  and  does  not  color  readily  with  imclear  stains.  As 
division  approaches,  these  chromatin  granules  become  aggregated 
together  in  certain  definite  areas,  forming  usually  a  convoluted  thread 
or  skein,  which  now  readily  takes  up  the  nuclear  stains  which  may  be 
used.  In  some  nuclei  this  skein  is  in  the  form  of  a  single  long  filament, 
in  others  the  chromatin  is  divided  up  from  the  first  into  a  series  of 
segments,  a  condition  which  soon  follows  in  the  case  of  a  single  fila- 
ment. By  transverse  fission  the  latter  breaks  up  into  a  series  of  seg- 
ments, the  'chromosomes,'  the  number  of  which  is  constant  for  each 
species  of  animal  or  ])lant.  Thus  in  the  common  mouse  there  are 
twenty-four,  in  the  onion  sixteen,  in  the  sea  urchin  eigliteen,  and  in 
certain  sharks  thirty-six.  The  numlx?r  may  be  quite  small,  as,  for 
example,  in  Ascaris,  a  cylindrical  jKirasitic  worm  inhabiting  tlie  alimen- 
tary canal  of  the  horse.  Here  the  number  is  either  two  or  four, 
depending  upon  the  variety  examined.  In  otlicr  forms  the  numlx^r 
may  be  so  large  as  to  render  counting  exceedingly  diflicult  or  im- 
possible. In  all  cases,  however,  one  fact  is  to  l)e  esp(MialIy  noted, 
viz.,  the  number  is  always  an  even  one,  a  striking  fact  which  finds  its 
explanation  in  the  phenomena  of  fertilization  to  be  discussed  later  on. 

"While  the  chromatin  is  collecting  into  the  form  of  the  chromo- 


*  Most  of  the  discussion  in  the  following  twnity  p:ii:«'s.  whet  licr  indicated 
by  quotation  marks  or  not,  i.s  takin  from  >hFarland'.s  essay  on  "'The 
Physical  Basis  of  Heredity  "  in  Jordan's  "  Footnotes  to  Kvolution  "  (1902). 


254  EVOLUTION   AND   ANIMAL   LIFE 

somes  the  nuclear  membrane  has  disappeared.  The  chromosomes 
soon  reach  their  maximum  staining  capacity,  and  appear  usually  as 
a  collection  of  rods  or  bands  of  deeply  staining  substance  l}dng  free 
in  the  cytoplasm. 

"While  this  is  taking  place  in  the  nucleus,  another  series  of  changes 
has  been  gone  through  by  the  centrosome  and  the  cytoplasm  im- 
mediately surrounding  it.  We  have  already  indicated  the  presence 
of  the  centrosome  as  a  minute  spherical  structure  lying  at  one  side 
of  the  nucleus.  This  body  assumes  an  ellipsoidal  form,  constricts 
transversely  into  a  dumbbell-shaped  figure,  and  divides  into  two 
daughter  centrosomes,  which  at  first  lie  side  by  side  but  soon  move 
apart.  Around  each  of  them  is  gradually  developed  a  stellate  figure 
composed  of  a  countless  number  of  delicate  fibrils  radiating  out  in  all 
directions  from  the  centrosome  as  a  center.  This  'aster'  or  'astro- 
sphere  '  is  at  first  small  in  extent,  but  grows  in  size  progressively  as  the 
two  centers  move  apart,  apparently  being  derived  from  a  rearrange- 
ment and  modification  of  the  threadlike  network  of  the  cytoplasm 
under  the  influence  of  the  centrosomes. 

"Between  these  two  asters,  which  lie  a  short  distance  apart  and 
at  one  side  of  the  nucleus,  a  spindle-shaped  system  of  delicate  fibrils 
may  often  be  made  out,  stretching  from  the  center  of  one  aster  to  that 
of  the  other.  This  fusiform  figure  is  termed  the  'central  spindle.' 
The  two  asters,  together  with  the  central  spindle,  form  what  is  termed 
the  'amp blaster'  or  the  'achromatic'  portion  of  the  karyokinetic 
figure.  The  two  series  of  changes  in  nucleus  and  cytoplasm,  which 
have  thus  far  gone  on  apparently  independently  of  each  other,  now 
become  closely  interrelated  in  that,  as  the  nuclear  membrane  dis- 
appears, a  system  of  fibrils  grows  out  from  each  astrosphere,  whicli 
attach  themselves  to  the  individual  chromosomes.  These  'mantle 
fibers'  insert  themselves  along  the  chromosomes  in  such  a  way  that 
each  segment  receives  a  series  of  fibrils  from  each  pole  of  the  amphi- 
aster,  the  two  series  being  attached  along  opposite  sides  of  the  chromo- 
somes. Under  the  influence  of  these  fibers,  probably  by  direct  pulling, 
the  chromosomes,  now  bent  into  V-  or  LT-shaped  loops,  tend  to  place 
themselves  in  a  circle  around  the  center  of  the  spindle,  transversely 
to  its  long  axis,  and  form  the  'equatorial  plate.' 

"The  changes  thus  far  constitute  the  'prophases'  of  the  division. 
The  '  metaphases '  following  these  consist  primarily  in  the  longitudinal 
splitting  of  each  chromosome  and  the  moving  a])art  of  the  halves. 
This  longitudinal  splitting  of  the  chromosome  into  two  equivalent 
parts  forms  the  most  important  act  of  the  whole  cell  division,  and  is 


FACTORS  IN  ONTOGENY 


i^iG.  145. — Cell  fission  in  the  salamander:  ^.Resting  nucleus  slagp.  centrtisome  pnrtly 
developed:  B,  skein  stage,  chromatin  visilile  as  a  convolute*!  hand,  the  con t nwomrs 
having  separated;  C.  the  nuclear  mcmhrane  having  .hsappoared.  an<l  a  frw  of  ihe 
chromosomes  lying  free  in  the  cytoplasm;  D.  central  spindle  rnmplete.  the  chr<»- 
mosomes  on  splitting  heing  drawn  to  the  spin.lle;  E.  metuphajsc;  F,  anaphuMr.  tho 
chromosomes  being  drawn  to  the  poles,     (.\fter  Driiner.) 


256  EVOLUTION  AND  ANIMAL  LIFE 

of  the  greatest  theoretical  significance.  By  it  the  chromatin  substance 
of  the  original  nucleus  is  equally  distributed  between  the  two  daughter 
nuclei,  so  that  each  receives  a  half  of  each  original  chromosome.  The 
elaborate  mechanism  and  consequent  expenditure  of  energy  involved 
in  this  careful  longitudinal  division  of  each  chromosome,  rather  than 
a  simple  mass  division,  such  as  might  be  brought  about  by  far  less  com- 
plicated means,  indicates  clearly  that  the  distribution  of  the  definite 
organization  of  the  chromatin  to  the  daughter  cells  is  of  primary 
importance,  a  conclusion  w^hich  is  further  strengthened  by  much 
evidence  too  extended  to  be  entered  upon  here. 

"In  the  'anaphases'  and  'telophases,'  which  include  the  closing 
stages  of  division,  the  daughter  chromosomes  migrate  along  the  fibers 
of  the  central  spindle  toward  its  poles,  perhaps  through  the  direct 
contraction  of  the  mantle  fibers  under  the  influence  of  the  centro- 
some,  though  this  and  many  other  points  regarding  the  forces  at  work 
must  be  left  for  future  investigation  to  decide.  Arrived  at  the  poles, 
V-shaped  chromosomes  become  grouped  in  a  star-shaped  figure,  the 
'aster,'  their  outer  ends  become  again  joined  together  in  the  form  of  a 
tangled  skein,  the  indi\ddual  chromatin  granules  separate  somewhat 
along  the  threads  of  the  linin  network,  their  deeply  staining  quality 
is  decreased,  and  a  new  nuclear  membrane  develops  around  each 
group  of  chromosomes.  Simultaneously  with  this  the  cytoplasm 
constricts  across  the  middle  of  a  somewhat  elongated  cell,  resulting 
in  complete  division  in  the  equatorial  plane  of  the  spindle,  and  two 
separate  daughter  cells  result.  Each  of  these  is  made  up  of  cytoplasm 
containing  a  centrosome  and  a  nucleus,  similar  in  all  respects  to  the 
parent  cell  from  w^hich  it  has  arisen. 

"A  simple  tabulation  of  the  changes  just  described  is  as  follows: 

Phases  of  Cell  Divisio>f  by  Karyokinesis 

C  1.  Resting  nucleus. 

I.     Prophases -j  2.  Skein  stage  of  chromatin. 

(.3.  Segmented  skein. 

.py      AT  f     V,  i  '^'  Equatorial     plate    and    splitting    of 

A.I.,     ivieuapnase j  , 

(  chromosomes. 

C  5.  IMovement   of  chromosomes  to  poles 

III.  Anaphases S  and  formation  of 

V  G.  Segmented  daughter  skeins. 

TT,.      ™  ,     ,  (7.  Reconstruction  of  nucleus. 

IV.  lelophases i  o    -ta-   •  •         ^      .     i 

(  8,  Division  of  cytoplasm. 


FACTORS   IN    OXTOdlONY  257 

"It  is  readily  seen  that  the  cuhniiiation  of  the  process  lies  in  tlie 
splitting  of  the  chromosomes  and  the  separation  of  their  component 
halves  to  form  the  two  new  dau«!;ht('r  nuclei." 

The  obvious  distinction  in  oapaeity  of  development  shown 
by  the  various  cells  wliicli  compose  an  animal's  body  leads  us 
to  ask  whether  we  can  distinguish  differences  a.'«sociated  with 
these  different  potentialities  in  the  line  structure  of  the  cells 
themselves,  and  especially  in  their  behavior  during  the  ])roces3 
of  multiplication.  For  the  fate  or  future  character  of  any 
cell  must  largely  depend  on  the  nature  of  its  origin,  the  character 
of  its  inheritance.  Now  in  some  cases  this  difference  in  poten- 
tiality of  the  undifferentiated  dividing  cells  is  plainly  shown 
by  differences  in  the  details  of  the  process  of  division.  A 
conspicuous  and  im])ortant  instance  of  this,  and  one  bearing 
directly  on  our  su])ject  of  tlie  relation  of  the  structure  and 
character  of  the  germ  j)lasm  to  the  fully  developed  organism, 
is  the  distinction,  usually  easy  to  make,  between  the  body  or 
so-called  somatic  cells  and  the  reproductive  or  germ  cells  of 
any  organism. 

"  Every  multicellular  organism  arises  by  a  process  of  division  from 
a  single  cell,  the  fertilized  germ  or  egg  cell,  which  in  turn  has  Ix'en  cut 
off  from  the  cells  of  a  preexisting  individual.  Out  of  the  group  of 
cells  which  result  from  the  continued  division  of  the  germ  cell  and  its 
descendants  arc  differentiated  the  various  tissues  and  organs  of  the 
body  through  which  the  vital  functions  are  carried  on.  Tliose  ti.ssues 
and  organs  which  perform  functions  pertaining  directly  to  the  existeru'c 
of  the  individual  have  been  termed  'somatic,'  and  their  constituent 
cells  the  'somatic'  or  body  cells,  in  contradistinction  to  the  repro- 
ductive tissues  or  cells  whose  function  concerns  the  contiiuiance  of 
the  species.  In  some  forms  these  groui)s  of  cells,  the  somatic  and  the 
reproductive,  become  isolated  from  each  other  quite  early  in  develop- 
ment; in  one  case,  indeed,  the  differentiation  of  rej)ro(luctive  cells 
from  the  somatic  ones  has  been  traced  hy  Hovcri  l»a(k  to  ti>e  first 
division  of  the  egg.  This  case  of  Ascaris  mcgalocephdUi  is  so  striking 
and  of  such  fundamental  theoretical  importance  that  it  nnist  not  U» 
passed  without  notice,  for  in  it  we  find  marked  differences  l)etwetM» 
the  somatic  and  reproductive  cells  in  their  nuclear  structure,  tlieir 
relative  amount  of  chromatin,  and  mode  of  division.  The  egg  of 
Ascaris  has  been  the  classical  object  for  cytological  studies  on  accguut 


258 


EVOLUTION   AND   ANIMAL   LIFE 


of  its  small  number  of  chromosomes  (two  in  variety  univalens,  four  L_ 
bivalens),   their  large   size,   and   the   diagrammatic   clearness  of  the 


Fig.  146. — Reduction  of  the  chromatin  in  the  cleavage  of  the  egg  of  Ascaris  megalo' 

cephala  var.  univalens.     (After  Boveri.) 

changes  which  take  place  in  division.  In  the  division  of  the  fertilized 
egg  cell  we  have  two  (in  univalens)  long  chromosomes  handed  over  to 
each  daughter  cell,    As  these  two  cells  in  turn  divide,  a  striking 


FACTORS  IX  r)XT(V;T:\V  250 

difference  is  seen  in  the  karyokinetic  fio;uro.s.  In  V\>^.  \U\,A,  such  a 
two-celled  stage  is  seen  from  the  i)ole;  in  B,  a  sliglitly  later  staple  in 
side  view  of  the  spindle.  In  the  upi)er  cell  of  .1,  the  division  is  of  the 
usual  form,  the  two  chromosomes  spht  longitudin.tlly,  and  thrir  two 
halves  travel  to  opposite  }>oles  of  the  sijindle  (B).  Hut  in  t  he  lower  cell 
this  is  not  the  case.  The  central  portion  of  the  two  cliromosomcs  is 
broken  up  into  a  large  number  of  minute  chromatin  granules  which 
divide,  and,  as  shown  in  B,  form  the  only  portion  of  the  chromosomes 
drawn  up  to  the  poles  and  entering  into  the  structure  of  the  resting 
nuclei  after  the  division  is  complete.  The  large  swollen  outer  ends  of 
the  clu-omosomes  are  cast  off  into  the  cyto})lasm  and  are  eventually 
absorbed,  playing  no  further  part  as  nuclear  structures.  C  shows  tin* 
fom--celled  stage,  in  which  a  marked  difference  in  the  size  of  the  nuclei 
of  the  upper  and  lower  cells  is  visible.  Lying  near  the  margins  of  the 
lower  cells  are  the  remnants  of  the  ends  of  the  chromosomes  which  have 
been  cast  off  in  the  di\ision.  In  D  the  four-celled  stage  is  shown  with 
the  karyokinetic  figures  of  the  next  division.  In  the  lower  cells  the 
spindles  are  seen  from  the  pole,  the  chromatin  is  present  in  the  re- 
duced amount,  in  the  form  of  small  granules.  In  the  upper  left-hand 
cell  the  two  full  chromosomes  are  seen,  each  split  longitudinally,  while 
the  upper  right-hand  cell  shows  a  repetition  of  the  reduction  i)henome- 
non — \iz.,the  central  portion  of  the  two  chromosomes,  broken  up  into 
granules,  alone  enters  into  the  spindle  figure,  the  outer  ends  Ijeing 
cast  off  into  the  cytoplasm,  where  they  suffer  a  similar  fate  to  those  of 
the  lower  cell  in  the  previous  division.  The  next  division  re;)eats  the 
process,  one  cell  retaining  the  two  full  chromosomes,  while  all  tlie 
others  have  the  reduced  amount.  This  takes  place  for  five  successive 
divisions  and  then  ceases;  from  the  one  cell  having  the  two  full  chro- 
mosomes the  reproductive  tissues  develop,  the  others  with  reduced 
chromatin  form  the  somatic  tissues.  Thus  is  accomplishe<l  a  visi])le 
structural  differentiation  of  the  nuclei  of  the  rei)roductive  cells  which 
distinguishes  them  shari)ly  from  all  the  somatic  tissues  in  Asrnris. 
We  shall  see  further  on  that  there  is  abundant  evidence  in  favor  of 
the  theory  that  the  nucleus — i.  e.,  the  chromatin — is  the  Ix'arer  of 
hereditary  influences  from  one  generation  to  the  next,  and  that  the 
specific  development  and  functions  of  each  iiKlividunl  cell  are  i\c- 
pendent  upon  the  specific  changes  which  take  place  in  the  chromatin 
of  its  nucleus.  In  this  light  the  almost  isolated  ea.se  of  A.scaris  pos- 
sesses a  value  and  interest  that  cannot  Ix'  overestimat<'d. 

"While  in  the  higher  forms  of  animals  and  i)lants  we  find  a  sharp 
differentiation  of  their  tissues  into  somatic  and  reproductive  or  germ 


260  EVOLUTION  AND  ANIMAL  LIFE 

cells,  we  must  bear  in  mind  that  not  in  all  forms  is  this  power  of  the 
reproduction  of  the  whole  organism  so  sharply  limited  to  the  germ 
cells  alone.  The  familiar  propagation  of  plants  by  cuttings,  the  re- 
generation of  complete  animals  from  small  portions  of  their  somatic 
tissues  in  many  lower  forms,  and  numerous  other  considerations  such 
as  these,  show  clearly  that  the  difference  between  the  powers  of 
somatic  and  germinal  cells  is  but  one  of  degree;  that  while  in  higher 
organisms  the  two  seem  sharply  defined  from  each  other,  a  series 
of  lower  forms  may  be  taken  which  T\all  show  the  intermediate  steps 
in  this  gradual  specialization  of  function. 

"In  the  unicellular  organisms  we  have  most  interesting  examples 
of  the  fundamental  facts  of  reproduction,  and  through  an  examina- 
tion of  these  we  may  gain  an  insight  into  the  more  compUcated  processes 
of  the  Metazoa.  Each  of  these  lowest  forms  consists  of  a  single  cell  in 
which  are  carried  out  in  a  generalized  way  the  complex  physiological 
functions  which,  in  many-celled  animals,  are  divided  up  among  cell 
groups.  In  reproduction  the  animal  simply  divides  into  two,  the 
division  of  the  nucleus  preceding  that  of  the  cytoplasm,  and  the  method 
is  usually  a  more  or  less  modified  karyokinetic  one.  This  mode  of 
multipHcation  continues  in  most  forms  for  a  certain  number  of  genera- 
tions, and  then  the  necessity  for  conjugation — i.  e.,  a  temporary  or 
permanent  fusion  with  another  individual — sets  in.  If  this  conjuga- 
tion be  prevented,  the  animal  soon  shows  increasing  signs  of  de- 
generation which  result  in  death.  This  'senescence'  of  the  powers  of 
growth  and  multiplication  can  only  be  checked  by  the  admixture  of 
new  nuclear  substances  from  an  entirely  different  individual  by  con- 
jugation. In  its  simplest  terms  this  process  is  found  in  Chilodon, 
according  to  Henneguy.  Chilodon  is  a  minute  fresh- water  infusorian, 
wliich  multiplies  for  a  considerable  period  of  time  by  transverse  di\ds- 
ion.  After  a  time,  however,  the  physiological  necessity  for  conjugation 
ensues.  The  animals  having  placed  themselves  side  by  side  in  pairs 
and  partly  fused  together,  the  nucleus  of  each  individual  divides 
into  two  portions,  one  of  which  passes  from  each  infusor  into  the  other 
to  unite  with  the  half  remaining  stationary.  The  two  then  separate, 
each  having  received  a  half  of  the  nucleus  of  the  other.  After  thus 
trading  experiences,  as  it  might  be  termed,  a  period  of  renewed  vigor 
and  activity  for  each  sets  in,  manifested  in  rapid  growth  and  multi- 
plication by  division,  producing  a  large  number  of  generations,  which 
continues  until  weakening  'vital  activities  indicate  the  periodically 
recurring  necessity  for  conjugation.  In  general,  among  the  Infusoria 
we  find  the  same  process  taking  place  in  regular  cyclical  order,  with 


FACTORS   IX   OXTOGEKl 


261 


more  or  less  complicated  variations  of  the  phenomena  just  outlined 
for  Chilodon.  In  all  of  them  the  aim  of  tiie  conjujjation  is  the  Siime 
the  exchange  of  a  certain  amount  of  nuclear  substance  Ijetween  the 
two  conjugating  individuals,  and  the  sam(^  physiological  effect  is 
reached,  a  rejuvenescence,  as  it  were,'of  the  two  organisms  Vvhich 
manifests  itself  in  renewed  vigor  of  growth  and  multiplication. 

"In  some  of  the  lowest  forms  of  unicellular  life — for  example,  tlie 
Schizomycetes  or  bacteria  and  their  allies — this  necessity  for  con- 
jugation    does     not 

appear  to  exist,  but  v"^-.  ^"^^^^^^\         A        /  /^  D 

for  the  vast  ma- 
jority of  forms  this 
cyclical  law  of  tle- 
velopment  holds 
good.  In  the  Pro- 
tozoa no  division 
into  somatic  and 
germinal  cells  is 
found,  both  func- 
tions being  united 
in  the  one  cell  which 
forms  the  whole 
body  of  the  or- 
ganism. In  the  Met- 
azoa,  however,  this 
differentiation  has 
taken  place;  the  germinal  cells  are  set  apart  for  the  preservation  of  the 
race;  the  somatic  cells  carry  on  their  various  functions  for  a  time, 
grow  old,  die,  and  disappear,  certain  of  the  germ  cells  alone  surviving 
in  the  production  of  new  individuals.  On  the  borderland  l)etween 
the  unicellular  and  the  multicellular  organisms,  however,  stand  cer- 
tain colonial  forms,  which  show  an  ex(|uisitely  graded  series  of  steps, 
from  the  conditions  of  unicellular  multiplication  to  those  of  the  nuilti- 
cellular  forms."     (McFarland.) 

In  the  many-celled  animals  the  egg  is  a  single  cell  laden 
with  a  large  amount  of  food  yolk,  and  made  up  of  nucleus  and 
cytoplasm  as  the  living  elements.  For  the  normal  development 
of  this  egg,  conjugation  with  another  g(M-m  cell,  derived  from  a 
different  individual,  is  usually  necessary.  This  germ  cell  is  the 
spermatozooid,  a  minute  cell  consisting  of  nucleus  and  centro 
18 


Fig.  147. — Gonium  pectorale,  a  simple  colonial  Protozoan, 
composed  of  sixteen  cells  holding  together  in  a  single 
layer  or  plate:  A,  The  whole  colony;  B,  a  single  coll;  <, 
eye  spot;  cl,  chloroplast;  n,  nucleus;  r,  vacuole.  (After 
Campbell.) 


262  EVOLUTION  AND  ANIMAL  LIFE 

some  with  a  small  amount  of  cytoplasm  modified  primarily  into 
an  organ  of  locomotion^  the  tail.  A  physiological  division  of 
labor  is  here  met  '^dth  which  admirably  meets  two  diametrically 
opposed  requirements.  The  one  of  these  demands  that  the 
conjugating  cells  be  higMy  motile,  and  consequently  small, 
in  order  that  they  may  be  able  to  come  together  in  the  w^ater 
in  w^hich  they  are  usually  set  free.  The  second  requires  that 
there  be  furnished  a  sufficient  amount  of  nutritive  material 
for  the  nourishment  of  the  embryo  until  it  arrives  at  a  stage  of 
growth  in  which  it  can  shift  for  itself.  These  tw^o  necessities 
have  been  met  by  the  physiological  division  of  labor  between 
the  two  conjugating  cells.  The  one,  the  sperm  cell,  has  become 
reduced  in  size  with  a  corresponding  gain  in  motihty,  the 
other,  the  egg  cell,  has  had  food  yolk  stored  up  in  it,  and  its 
consequent  increased  size  prevents  any  more  than  a  very  slight 
degree  of  independent  movement,  if  any.  Different  stages  of 
these  modifications  may  be  met  wdth  among  unicellular  forms, 
as  illustrated  in  Pandorina,  Eudorina,  and  Volvox,  to  which 
might  be  added  many  others.  In  Pandorina  the  conjugating 
cells  are  of  nearly  equal  size,  in  Eudorina  an  intermediate  con- 
dition is  reached,  wdiile  in  Volvox  the  egg  and  sperm  cells  are 
sharply  differentiated  in  size  and  motility.  Again,  in  the  first 
two  and  their  allies  all  of  the  cells  are  at  first  vegetative  and 
afterward  reproductive,  while  in  Volvox  the  definite  separation 
into  vegetative  or  somatic,  and  reproductive  or  germinal  cells 
makes  its  appearance. 

We  arrive  then  at  the  conclusion,  from  the  consideration 
of  these  and  many  other  lines  of  evidence,  that  the  germ  cells 
were  primitively  exactly  ahke,  and  that  the  differences  between 
them  have  arisen  in  the  process  of  differentiation  along  tw^o 
separate  lines.  Furthermore,  it  is  clear  that  the  difference? 
between  the  two  sexes,  which,  become  strongly  characterized 
in  the  higher  vertebrates,  are  all  of  a  purely  secondary  nature. 

In  their  early  development  the  germ  cells  are  indistinguish- 
able from  each  other,  and  both  pass  through  certain  stages, 
preliminary  to  their  union,  w4iich  are  essentially  alike.  The 
animal  egg  is  a  large,  more  or  less  spherical  cell,  enveloped 
usually  by  certain  membranes,  containing  a  large  nucleus  and 
cytoplasm.  The  vast  bulk  of  the  egg  cell,  however,  is  made 
up  of  inert  food  material  in  the  form  of  yolk  granules,  which 
are  stored  up  in  it  as  nourishment  for  the  developing  embryo. 


FACTUKS   IX   OXTOGEXY 


263 


"^  4f  W 


L 


M^^ 


q*>\\  **  II  /  / 


0 


c-;i' 


F 


•jG.  148. — Maturation  of  the  egj?  of  Cyclops  (the  full  number  of  cnromnsomes  is  not 
shown):  A,  Chromosomes  already  split  longitudinally;  B,  chromatin  masses  with 
indication  of  transverse  fission  to  form  the  tetrads;  C,  the  younR  tetrads  arran^inR 
themselves  on  the  first  polar  l)ody  spindle;  D,  tetrads  in  first  body  spindle;  E, 
separation  of  the  dyads  in  the  same;  F,  position  of  the  dyads  in  the  second  polar 
body  spindle,  the  first  polar  body  being  reaUy  above  the  margin  of  the  egg.  (After 
Riickert.) 


264 


EVOLUTION  AND  ANIMAL  LIFE 


The  nucleus,  or  germinal  vesicle,  is  large,  and  contains  a  net- 
work of  chromatin  together  with,  one  or  more  conspicuous 
nucleoli. 

There  are  three  periods  usually  recognized  in  the  develop- 
ment of  the  egg  cell,  viz.:  (1)  The  period  of  multiphcation;  (2) 
the  period  of  growth;  and  (3)  the  period  of  matm-ation.  The 
first  period  is  characterized  by  a  continued  series  of  divisions 
of  the  primitive  reproductive  cell  and  its  descendants,  wliich 


Fig,  149. — Formation  of  the  chromatins  and  tetrads  in  the  spermatogenesis  of  Ascaris 
megalocephala.  In  A-C,  the  whole  cell  is  shown;  in  D-H,  only  the  nucleus.  (After 
Brauer.) 


produces  a  large  number  of  "ovogonia.'^  Succeeding  this  is 
a  period  of  growth  in  which  the  ovogonia  increase  greatly  in 
size,  mainly  through  the  production  and  storing  up  of  food 
yolk.  At  the  close  of  this  period  the  germ  cell,  now  termed  a 
"primary  ovocyte,''  enters  upon  the  maturation  period,  in 
which  it  undergoes  two  divisions  in  rapid  succession,  by  means 
of  which  two  minute  cells,  the  polar  bodies,  are  cut  off  from 
■'cm  egg.  Through  these  two  divisions  the  number  of  chromo- 
someis  in  the  egg  nucleus  is  reduced  to  one  half  that  which  is 
found  in  the  other  cells  of  the  body.  The  first  polar  body  also 
usually  divides,  and  thus,  at  the  close  of  the  period  of  matura- 
tion, four  cells  result:  one  large  mature  egg  cell,  ready  for  the 
fertilization  which  initiates  the  development  of  the  embryo, 
and  three  minute  polar  bodies,  which  are  to  be  regarded  simply 
as  rudimentary  eggs.    The  uuclei  of  these  four  cells  are  exactly 


FACTORS   IN   ONTOGENY 


265 


alike  in  that  they  all  contain  the  same  number  of  chromosomes, 
i.  e.,  one  half  the  number  in  the  somatic  cells  of  the  individual. 
The  difference  in  size  is  due  simply  to  the  concentration  of  the 
food  yolk  and  most  of  the  cytoplasm  in  one  of  the  cells;  the 
other  three  degenerate,  being  sacrificed  to  the  production  of 
an  egg  cell  with  the  largest  possible  supply  of  nutritive  sub- 
stance in  it. 

In  the  development  of  the  sperm  cell  (Figs.  149, 150),  we  find 
an  exactly  parallel  series  of  stages,  the  end  results,  however, 
differing  much  in  size. 
The  mature  sperma- 
tozoon is  an  exceed- 
ingly minute  cell,  con- 
sisting typically  of  a 
cylindrical  or  conical 
''^head"  containing  a 
nucleus,  a  short  cyto- 
p  1  a  s  m  i  c  "middle 
piece,''  and  a  long 
vibratile  "tail/'  an 
organ  of  locomotion 
differentiated  out  of 
the  cytoplasm  of  the 
cell  from  which  the 
spermatozoon  is  de- 
rived.    The  stages  of 

multiplication,  growth,  and  maturation  are  passed  through  in 
the  development  of  the  spermatozoon  in  the  same  order  as 
in  the  egg  development,  save  that  the  period  of  growth  does 
not  include  the  storage  of  food  yolk  in  the  primary  sperma- 
tocyte, and  the  two  divisions  of  the  maturation  stages  are 
equal  ones,  resulting  in  the  production  of  four  cells  of  the 
same  size,  each  of  which  develops  into  a  comi)lete  sperma- 
tozoon. 

The  accompanying  diagrams  of  Fig.  151,  taken  from  Boveri, 
illustrate  clearly  the  homologies  existing  between  the  life 
histories  of  the  two  sorts  of  germ  colls.  The  earlier  stages  of 
ovogonia  and  spermatogonia  are  indistinguishable  from  each 
other;  later  in  the  period  of  growth  the  increase  in  size  of  an 
ovocyte  marks  it  off  from  the  minute  spermatocyte,  but  this 
distinction  is  merely  one  due  to  nonliving  food   material,  and 


Fig.  150. — First  (A-C)  and  second  {D  H)  matura- 
tion of  the  spermatocytes  of  Ascaris  megalocephala. 
(After  Brauer.) 


266  EVOLUTION  AND  ANIMAL  LIFE 

in  nowise  affects  the  fundamental  identity  of  the  two.  In  the 
maturation  period  the  number  of  chromosomes  in  the  nuclei 
of  both  egg  and  sperm  is  reduced  one  half — on  the  one  hand, 
the  ripe  egg  cell  and  three  rudimentary  egg  cells  (the  polar 
bodies)  being  formed;  on  the  other,  four  equal  "spermatids" 
are  produced,  which  develop  into  four  mature  spermatozoa. 
The  contrast  in  size  which  exists  between  the  two  mature  re- 
productive cells  is  enormous,  the  spermatozoon  in  some  cases 
containing  less  than  tttoVoo  (Wilson),  and  in  extreme  cases  less 
than  To WxToo IT  (Hertwig)  of  the  volume  of  the  egg  cell. 


A .  A  i\^^ 


Fig.  151. — At  left,  diagram  illustrating  the  development  of  the  spermatozoon;  at  right, 
diagram  illustrating  the  development  of  the  egg.     (After  Boveri.) 

A  discussion  of  the  method  by  which  the  reduction  of  the 
chromosomes  in  the  germ  nuclei  is  brought  about,  may  profit- 
ably be -deferred  until  the  essential  features  of  fertihzation 
have  be^n  examined.  The  phenomena  of  the  fusion  of  egg  and 
sperm  can  best  be  studied  in  some  such  form  as  the  sea  urchin, 
in  which  the  egg  is  very  small,  and,  in  some  species,  quite 
transparent.  As  fertilization  takes  place  free  in  the  sea  water, 
the  germinal  cells  being  cast  out  fK)m  the  parents,  it  is  possible 
to  collect  the  eggs  and  sperm  separately  from  mature  in- 
dividu^ils  and  bxing  them  together  in  small  dishes  of  sea  water, 
r.nd  at  sucli  times  as  may  suit  one's  convenience.  Then  in  the 
r.ving  egg  much  of  the  process  may  be  followed  under  the 
i.yL/oncopc,  and  properly  prepared  sections  of  the  eggs,  killed 


FACTORS   IN    ONTOGENY 


26: 


by  reagents  at  the  various  stages,  enable  conclusions  to  be 
drawn  as  to  matters  of  minute  detail. 

I'ig.  153,  A  to  F,  presents  a  series  of  diagrams,  taken  from 
Boveri,  illustrating  the  jjrincipal  facts  in  the  process  of  ferti- 
lization. In  .1,  the  egg  is  represented  with  its  clear  nucleus 
in  the  center,  surrounded  by  the  egg  membrane.  Clustered 
around  the  peripliery  are  a  number  of  spermatozoa  endeavoring 
to  find  their  way  into  the  substance  of  the  egg.  On  the  right- 
hand  side  in  the  figure  one  has  penetrated  the  membrane  and 
is  shown  passing  into  tlie  egg  cytoplasm,  which  puts  forth  a 
small  conical  prominence  to  meet 
it.  As  soon  as  the  head  of  one 
sperm  enters  the  egg  cytoplasm  a 
new  membrane  is  formed  around 
the  egg  which  effectually  prevents 
tlie  entrance  of  any  others.  The 
head  ai:d  middle  piece  penetrate 
into  .he  egg,  the  tail  usually  re- 
maining imbedded  in  the  mem- 
brane, where  it  soon  degenerates. 
A  few  momc^nl  s  after  the  sperm  has 
entered,  a  system  of  radiations 
appears  around  the  middle  piece 
which  develops  into  an  aster  sur- 
rounding the  centrosome  of  the 
sperm   (B).     The    sperm    nucleus 

swells  up  and  rapidly  increases  in  size,  its  chromatin  changing 
from  the  compact  condition  in  which  it  is  arranged  in  the 
sperm  head  to  a  reticulate  condition  (C).  The  chromatin  re- 
ticulum of  the  egg  nucleus  becomes  also  more  clearly  visible. 
Sperm  aster  and  sperm  nucleus  now  move  in  toward  the 
egg  nucleus,  the  aster  usually  preceding.  As  the  nuclei  ap- 
proach, the  sperm  nucleus  increases  still  more  in  size  until 
it  becomes  indistinguishable  from  the  egg  nucleus  (C).  The 
chromatin  network  of  each  now  breaks  up  into  a  numl^er 
of  chromosomes,  one  half  of  the  num])er  found  in  the  som- 
atic cells,  and  the  nuclei  come  into  contact,  fusing  together 
in  some  cases.  As  in  the  sea  urchin.  Echinus,  the  numl)er  of 
chromosomes  is  eighteen,  nine  would  therefore  be  found  in 
the  germ  nuclei;  for  the  sake  of  clearness  and  simplicity 
but  two  are  represented  in  the  diagram^  those  of  the  sperm 


Fig.  152. — Egg  of  the  worm,  Myzo- 
stoma  glabrum,  being  fertilized  by 
spermatozoon.      (After  Wheeler.) 


268 


EVOLUTION   AND   ANIMAL   LIFE 


Fig.  153. — Diagrams  illustrating  the  fertilization  of  the  egg:  A,  Egg  surrounded  by- 
spermatozoa;  on  the  right,  one  has  just  penetrated  the  egg  membranes  and  is  en- 
tering the  egg  cytoplasm;  egg  nucleus  in  the  center.  B,  Egg  nucleus  with  chromatin 
reticulum  on  the  left;  on  the  right,  the  sperm  nucleus  preceded  by  its  centrosome 
and  attraction  sphere.  C,  Egg  nucleus  on  the  left,  sperm  nucleus  on  the  right  of 
the  center  of  egg;  aster  fibrils  preceding  the  fission  of  the  centrosome.  D,  The 
centrosome  has  divided,  the  two  attraction  spheres  separate  to  form  the  first 
cleavage  of  the  spindle;  the  chromosomes  of  the  egg  and  sperm  nuclei  clearly  visible 
and  distinguishable  (in  the  figure  the  egg  chromosomes  are  black,  the  egg  sperm 
chromosomes  shaded).  E,  First  cleavage,  showing  spindle  with  splitting  chromo- 
somes. F,  Completion  of  first  cleavage,  two-celled  stage,  each  nucleus  showing  four 
chromosomes,  two  from  the  egg  and  two  from  the  sperm.     (After  Boveri.) 


FACTORS   IN   ONTOGENY  269 

nucleus  being  slightly  shaded  while  those  of  the  egg  nucleus 
are  black. 

The  centrosomc  divides  together  with  its  aster  (D),  the  two 
daughter  centrosomes  move  apart  to  opjjosite  poles  of  the  egg, 
and  the  tA^^ical  ampliiaster  of  cell  division  is  formed  (E),  the 
nuclear  membranes  disa})i)earing  and  the  chromosomes  being 
drawn  together  into  the  equatorial  })late  where  each  splits 
longitudinally.  The  halves  are  drawn  by  the  mantle  fn)rils 
toward  the  opposite  poles,  and  the  eg,g  divides  transversely 
into  two  cells  (F).  This  process  of  division  is  repeated  con- 
tinuously in  each  of  the  resulting  generations  of  cells,  and 
from  the  mass  of  cells  thus  formed  develops  the  new  organism. 
Each  cell  in  the  tw^o-celled  stage  has  received  half  of  its 
chromosomes  from  the  egg  nucleus  and  half  from  the  sperm, 
thus  containing  equal  amounts  from  each  parent.  The  centro- 
some,  which,  as  we  have  seen,  is  to  be  regarded  as  the  dynamic 
center  of  the  cell  division,  comes  from  the  spermatozoon  alone; 
the  egg,  on  the  other  hand,  furnishes  the  yolk  and  i^ractically 
all  of  the  cytoplasm. 

After  this  preliminary  outline  of  the  facts  of  fertilization,  we 
are  in  a  better  position  to  understand  the  significance  of  a  process 
which  occurs  in  the  development  of  both  egg  and  sperm  cells, 
namely,  the  reduction  of  the  chromosomes.  The  necessity  for 
such  a  reduction  is  evident  from  a  moment's  reflection.  We 
have  seen  that  the  number  of  chromosomes  in  the  nucleus  is 
a  constant  and  typical  one  for  each  animal  and  plant  species 
so  far  as  known.  As  fertilization  consists  in  the  union  of  two 
cells  in  one,  from  w^hich  the  young  organism  develops,  it  is 
plain  that,  were  there  no  reduction,  the  number  of  chromo- 
somes would  be  doubled  in  each  succeeding  generation.  How- 
ever simple  this  necessity  for  reduction  may  appear,  the  mi- 
nutiae of  the  processes  through  which  it  is  brought  about,  and 
the  theoretical  significance  of  these  facts,  form  one  of  the  most 
involved  prol^lems  of  biology  to-day.  In  a  few  forms,  especially 
among  the  lower  Crustacea,  the  facts  of  the  reduction  are  clear 
and  relatively  simple;  in  other  forms  they  thus  far  stand  in 
direct  contradiction,  and,  for  the  present,  a  comprehensive 
explanation  applicable  to  all  forms  must  be  left  to  further 
investigation. 

The  significance  of  reduction  turns  upon  tlie  conception 
of  a   definite   organization   and    in(hvi(hi:dit  \-    in    tlie   diroino- 


270 


EVOLUTION   AND   ANIMAL   LIFE 


somes  and  the  assumption  that  they  represent  the  physical 
basis  of  heredity — i.  e.,  that  they  influence  and  determine  into 
what  the  fertihzed  egg  shall  develop.  Fifteen  years  ago 
Wilhelm  Roux  showed  with  convincing  clearness  that  the 
complicated  facts  of  nuclear  division^  the  careful  longitudinal 
halving  of  the  chromatin  thread  and  its  equal  distribution 
between  the  two  daughter  cells,  can  be  explained  only  on  the 
basis  that  the  chromosomes  possess  different  structure  in  dif- 
ferent parts  of  their  extent,  and  that  these  structures,  repre- 
senting tendencies  in  development,  are  distributed  in  definite 
ways  to  the  daughter  cells.  Were  this  not  the  case,  a  simple 
direct  mass  division  of  nucleus  and  cytoplasm  instead  of  the 

complicated  process  of 
karyokinesis  with  its 
consequent  much  greater 
expenditure  of  energy 
would  serve  all  pur- 
poses. 

In  the  hght  of  this 
probable  individuality 
and  morphological  or- 
ganization of  the  chro- 
mosomes, the  method  of 
their  reduction  in  num- 
ber, preparatory  to  the  fusion  of  their  germ  cells,  becomes 
of  the  greatest  significance;  to  those  who  may  deny  this  in- 
dividuality and  definite  architecture,  the  phenomena  can  have 
no  great  importance  save  as  concerns  a  general  mass  reduc- 
tion in  the  amount  of  the  chromatin  present  in  the  germ  nu- 
clei. It  may  be  assumed  as  true,  in  the  majority  of  cases 
now  accurately  known,  that  the  reduction  takes  place  some- 
where in  or  near  the  last  two  divisions  of  the  germ  cells  previous 
to  their  fusion — that  is,  in  the  egg,  in  the  divisions  forming 
the  polar  bodies,  and  in  the  sperm,  in  the  last  two  divisions  of 
the  spermatocyte  which  produce  the  four  spermatids  out  of 
which  develop  as  many  mature  spermatozoa.  The  phenomena 
are  exactly  homologous  in  both  cases,  as  has  already  been 
pointed  out,  differing  only  in  the  minor  details  which  do  no'- 
affect  the  end  result. 

Two  peculiar  features  mark  these  divisions  off  from  all  the 
others  which  precede  and  follow  them.     One  of  these  is  the 


Fig.  154. — Formation  of  the  polar  bodies  shown 
diagrammatically.     (After  Korschelt  and  Heider.) 


FACTORS   IN   ONTOGENY 


271 


absence  of  an  intermediate  resting  stage  between  them,  the 
second  division  following  immediately  upon  the  first  without 
the  reconstitution  of  the  chromosomes  into  the  skein  stages. 
The  second  peculiarity  lies  in  the  fact  that  the  chromatin  (now 
the  individual   chromosomes)  appears  in  one  half  the  typical 


R 


»5-$jy 


**»» 


Fig.  155. — Reduction  of  chromosomes  in  the  spermatogenesis  of  Ascaris  megalocephaJa 
var.  hivalens:  A,  Nucleus  of  a  si)ermatogoniuin,  the  typical  number  of  chromo- 
somes (4)  shown,  each  split  longitudinally  preceding  the  nucleus  fission;  B,  young^ 
splitting  primary  spermatocyte,  two  tetrads  present,  each  with  body  double  from 
longitudinal  splitting  of  a  chromatin  thread;  C,  the  tetrads  in  the  equatorial  stage 
of  fission;  D,  separation  of  the  dyads;  E,  the  djads  in  succeeding  fission  of  the 
secondary  spermatid;  F,  completion  of  the  fission  of  the  same,  each  cell  (spermatid) 
contains  the  reduced  number  of  chromosomes  (2).     (After  Brauer.) 


number  of  the  chromosomes  in  the  first  division,  and  is 
usually  arranged  in  "tetrads,'^  or  groups  of  four  rounded, 
deeply  staining  bodies  connected  by  linin  fibers.  These  tetrads 
are  always  one  half  the  number  of  the  original  rod-  or  thread- 
like chromosomes.  Thus  in  Fig.  155,  A  represents  a  sperma- 
togonium nucleus  of  Ascaris  with  the  four  chromosomes, 
showing    tlic    longitudinal    splitting    preparatory    to    division. 


272  EVOLUTION  AND  AXIMAL   LIFE 

B  represents  an  early  spindle  stage  in  the  division  of  the 
primary  spermatocyte,  in  which  not  four  bandhke  chromo- 
somes, but  two  tetrads,  or  chromatin  groups  or  four  rounded 
bodies  are  found.  C  to  F  show  clearly  the  further  steps  in 
the  spermatogenesis.  In  C  the  tetrads  are  grouped  in  the 
equatorial  plate,  and  in  D,  in  the  closing  stages  of  the  first  di- 
vision into  two  spermatotytes,  each  tetrad  has  divided  into 
two  "dyads,''  which  are  drawn  to  the  poles,  and  the  division 
of  the  cell  body  follows.  Without  an  intervening  rest  stage 
each  spermatocyte  now  divides  again,  as  in  E  and  F,  each 
dyad  being  separated  into  halves,  so  that  in  the  spermatids  of 
F  but  two  chromatin  masses  are  present.  Thus  the  tetrads 
of  the  primary  spermatocyte  are  divided  up  among  the  four 
spermatids,  so  that  each  of  the  latter  receives  one  fourth  of 
each  tetrado  Since  later  stages  show  that  the  two  chromatin 
masses  in  each  spermatid  of  F  represents  two  chromosomes,  we 
see  that  the  number  of  chromosomes  has  been  reduced  from 
the  four  in  A  to  the  two  in  F. 

Manifestly  the  key  to  the  explanation  lies  in  the  relations 
which  exist  between  the  four  chromosomes  of  A  and  the  tetrads 
of  B.  The  two  divisions  consist  merely  in  the  distribution  of 
the  already  separated  parts  of  the  tetrads ;  in  the  rearrange- 
ment of  the  four  chromosomes  into  the  two  tetrads  lies  the 
possibility  of  the  reduction  which  is  carried  out  by  the  fol- 
lowing divisions.  The  problem  thus  resolves  itself  into  the 
question.  What  is  the  nature  of  each  tetrad?  Is  it  made  up 
of  a  single  chromosome?  of  two?  of  four?  or  have  the  constituent 
parts  of  the  original  four  chromosomes  become  so  completely 
rearranged  and  redistributed  that  their  identity  as  such  is 
completely  lost? 

Tm-ning  for  a  moment  to  the  lower  Crustacea,  we  find  among 
the  Copepods  forms  admirably  suited  for  the  careful  following 
out  of  the  changes  taking  place  in  the  rearrangement  of  the 
chromosomes  into  the  tetrads.  To  Riickert  we  owe  the  clearest 
account  of  the  process  as  exhibited  in  the  egg  maturation  of 
Cyclops.  Here  the  normal  number  is  twenty-two,  or  perhaps 
twenty-four,  the  minute  size  rendering  counting  difficult.  Fig. 
148,  A  to  F,  taken  from  Riickert,  gives  the  essential  points  of 
the  formation  of  the  tetrads  and  their  following  divisions,  not 
all  the  chromosomes  being  represented.  In  A  the  chromatin 
filament   has  broken  up  into   one  half  the   usual  number  of 


FACTORS   IN   ONTOGENY  273 

segments  (cliromosomes),  and  each  sliows  the  precocious  longi- 
tudinal sphtting.  These  segments  shorten  up  into  the  dou))le 
rods  of  B,  which  in  C  are  being  arranged  in  the  developing 
spindle.  A  comparison  of  these  three  figures  will  show  clearly 
that  each  chromatin  segment  has  divided  both  longitudinally 
and  transversely,  its  parts  shortening  and  arranging  them- 
selves in  tetrad  formation  of  D.  The  first  division  following 
separates  the  tetrad  along  the  longitudinal  plane  of  its  former 
.sphtting  {E)  and  the  second  division  along  the  transverse 
plane  {F). 

In  Cyclops  then,  the  tetrads  are  formed  by  the  chromatin 
thread  of  the  resting  nucleus  breaking  up  into  one  half  the 
usual  number  of  segments,  and  each  of  these  in  turn  dividing 
longitudinally  and  transversely.  A  tetrad  here  is  made  up  of 
two  chromosomes  slightly  united  end  to  end  and  spHt  longi- 
tudinally. Thus  if  abcdef  .  .  .  n  represent  the  unsegmented 
filament  of  the  resting  nucleus,  a-h-c-d-e-f  would  show  its 
breaking  up  into  the  normal  number  of  chromosomes  which 

7  7  P 

split  lengthwise,  forming  -)  ^y  -j  -^y  ->  v  in  the  equatorial  plate. 

In  the  Cyclops  nucleus  of  Fig.  A  the  filament  has  separated 
into  the  segments  ab-cd-ef  .   .  .  n,  each  of  w^hich  has  spht  longi- 

tudinallv  into  —  >  — :>  — .^  etc.,  and  its  transverse  division,  sub-- 

ab   cd   ef         '  ' 

sequently  becoming  more  apparent,  gives  to  each  tetrad  the 

etc.      By   the   first   division    in    the 


a\h 


d 
d! 


f 
7 


composition   -7? 
ab 

longitudinal  plane,  each  daughter  cell  receives  a  half  of  each 

chromosome;  in  the  second,  however,  in  the  vertical  plane, 

this  is  not  the  case,  as  can  be  readily  seen.     This  is  clearly  a 

c{ualitative    division,    and   the   daughter    cells   receive    unlike 

chromosomes.     This  forms  the  "reducing  division''  in  Weis- 

mann's  sense,  and  as  such  is  a  most  beautiful  demonstration 

of  his  postulated  reduction  of  the  ancestral  plasm. 

In  Ascaris,  however,  the  evidence  is  just  as  clear  that  no 
reducing  division  in  Weismann's  sense  takes  place,  though 
the  actual  number  of  the  chromosomes  is  also  reduced. 

Boveri  has  shown  for  the  e^^  and  Brauer  for  the  sperm 
that  the  tetrads  arise  by  a  double,  longitudinal,  splitting  of 
the  chromatin  filament  which  later  breaks  into  two  segments. 
Thus  abed  >vould  again  represent  the  unsegmented  filament, 


ah   cd 
ab  cd 


cd 
cd 


274  EVOLUTION   AND   AXLMAL   LIFE 

ri    h    c   d 
a-b-c-d  the  individual  chromosomes,  and  -j  y^  -j  -'  their  splitting 

abed 

longitudinally    in    ordinary    division.     In    the    maturation    of 

the  egg  and  in  spermatogenesis,  hov/cver,  the  thread  segments 

into  ab,  cd,  and    splits   twice  longitudinally  into  — 

the  two  tetrads  of  B  in  Fig.  155.  The  reduction  of  chromatin 
here  is  only  a  reduction  in  mass  and  not  a  qualitative  one,  in 
Weismann's  sense,  as  in  the  Crustacea  and  insects.  In  Ascaris 
the  actual  reduction  in  number  of  chromosomes  takes  place 
in  the  nucleus  previous  to  the  maturation  divisions  of  the 
ovocyte  and  spermatocyte  respectively.  In  Cyclops  the  for- 
mation of  the  tetrads  is  merely  a  pseudo-reduction,  the  actual 
reduction  taking  place  in  the  second  division,  which  gives  rise 
to  the  mature  egg  on  the  one  hand,  or  the  spermatids,  w^hich 
develop  into  the  spermatozoa,  on  the  other. 

One  fundamental  fact  is  clear  in  these  divergent  accounts. 
The  number  of  chromosomes  is  reduced  in  both  sorts  of  the 
germinal  cells  as  a  preliminary  to  their  union.  Whether  there 
is  likewise  a  qualitative  distribution  of  the  chromatin  elements 
remains  for  future  investigation  to  decide.  From  the  facts  of 
ordinary  cell  division  we  have  seen  that  the  chromatin  of 
the  nucleus  is  to  be  regarded  as  the  bearer  of  hereditary  qualities 
in  the  cell.  The  phenomena  of  fertilization  greatly  increase 
this  probability.  The  offspring  resembles  both  of  its  parents, 
and  the  paternal  tendencies  can  be  conveyed  in  the  minute 
spermatozoan  head  alone,  which  is  constituted  almost  entirely 
of  chromatin.  The  scrupidous  exactitude  with  which,  in  both 
germ  cells,  the  chromosomes  are  reduced  to  one  half  the  normal 
number  preparatory  to  the  union  of  the  pronuclei  in  fertiliza- 
tion, and  the  distribution  of  the  paternal  and  maternal  chro- 
matin equally  to  the  resulting  cells  of  cleavage,  lenc!  "dded 
weight  to  the  theory. 

The  development  of  the  fertilized  germ  cell  into  the  ccrn- 
plete  organism  is  discussed  in  the  preceding  chapter  as  also 
is  the  significance  of  sex.  This  significance  in  the  light  of  actual 
processes  of  germ-cell  formation,  maturation,  and  fertilization 
is  seen  to  be  very  important  in  relation  to  the  phenomenon 
of  variation,  a  phenomenon  or  fact  which  we  have  already 
learned  to  recognize  as  the  absolutely  essential  basis  of  all 
organic  evolution. 


FACTORS  IN   ONTOGENY 


275 


o 


'IG.  15G. — -A,  Normal  larva  of  Echinus  microtuberculatus.  front  viev,-;  5,  the  same,  side 
view;  C,  normal  larva  of  Sphaerechinus  granularia,  front  view;  D,  the  same,  side 
view.     (After  Boveri.) 


276  EVOLUTION  AND  ANIMAL  LIFE 

Whether  the  new  individual  to  be  exists  in  the  germ  cell 
as  a  more  or  less  nearly  completely  preformed  embryo  needing 
only  to  expand,  unfold,  and  grow  to  be  the  fully  developed 
new  creature,  or  whether  the  fertihzed  egg  cell  is  a  bit  of  prac- 
tically undifferentiated  protoplasm,  endowed  with  a  hmited 
and  specific  potentiahty,  but  depending  for  its  marvelous  out- 
come chiefly  on  extrinsic  imposed  influences — this  question 
has  been  a  matter  of  contention  since  the  beginning  of  the 
study  of  generation  and  development. 

From  our  scrutiny  of  the  phenomena  of  mitosis,  it  is  ap- 
parent that,  while  the  germ  cell  is  certainly  considerably 
differentiated  as  regards  its  fine  structure,  on  the  other  hand  it 
as  certainly  contains  no  preformed  embryo  of  the  individual 
into  which  it  is  to  develop,  as  the  old  school  of  preformationists 
held.  But  the  testimony  from  mitosis  by  no  means  settles  the 
controversy  between  the  modern  preformationists  and  the 
modern  epigenesists.  This  rages  hotly,  and  furnishes  a  great 
incentive  to  the  pushing  on  of  the  study  of  development. 

What  is  most  interesting,  perhaps,  about  this  present-day 
embryological  study  is,  perhaps,  its  method.  Where  hereto- 
fore the  stud}^  of  development  has  been  almost  purely  descrip- 
tive and  comparative,  as,  indeed,  all  biological  study  has,  the 
modern  embryologist  is  an  experimenter.  Experiment,  the 
method  of  the  study  of  inorganic  nature,  is  being  resorted  to 
and  relied  on  for  the  determination  of  biological  problems,  and 
in  particular  that  one  that  has  for  its  subject  the  seeking  of 
the  factors  and  actual  causes  of  individual  development. 
This  has  been  aptly  named  preformation  versus  epigenesis. 
It  might  also  pertinently  be  called  intrinsic  versus  extrinsic 
factors  or,  more  broadly,  vitalism  versus  mechanism. 

The  new  phase  or  mode  of  the  study  of  development  has 
been  variously  called  developmental  mechanics,  experimental 
development,  or,  more  broadly,  experimental  morphology, 
because  the  experimental  method  has  been  extended  to  the 
study  of  phenomena  not  strictly,  or  at  least  not  usually  in- 
cluded-in  the  immature,  or  developing  stage  of  the  animal's 
life;  the  study  of  regeneration,  of  reactions  to  stimuli,  and  of 
reflexes  and  movements  in  general,  has  all  been  illuminated 
by  the  decisive  results  of  the  substitution  of  experiment  for 
haphazard  observation  in  nature.  And  the  further  extension 
of  experimental  and  statistical  modes  of  investigation  to  the 


FACTORS  IN  OXTOGEKY 


277 


G 


Fig.  157. — A,  Hybrid  larva  {Sphrcr echinus  ?  and  Echinus  i),  front  view;  B,  the  same 
from  side  view;  C,  hybrid  larva,  Spharechinus  ?  (nonnucleated  egg  formation; 
and  Echinus  i  ,  of  the  type;  D,  the  same  larva  in  side  view.     (After  Boveri.) 


19 


278 


EVOLUTION  AND  ANIMAL  LlFl<l 


"grand  problems"  of  heredity  and  variation,  already  well 
entered  upon,  bids  fair  to  produce  the  moMt  rapid  and  real 
advance  that  has  yet  been  made  to\vard  tlu;  goal  of  solving 
some  of  the  mystery  which  has  so  far  enwi-apped  these  funda- 
mental phenomena  of  life. 

To  return  to  our  special  problem  of  preformation  or  epi- 
genesis,  it  must  be  said  at  the  outset  that  the  evidence  touching 
it,  which  has  so  far  been  derived  from  experiment,  is  distinctly 
conflicting.     For  example  the  frog's  egg   (which  has  been  a 

classic  V or siichs object  in  this 
study),  when  treated  after  its 
first  cleavage  so  that  one  of  its 
two  blasto  meres  (daughter  cells 
of  the  original  fertilized  egg  cell) 
is  killed,  develops  half  a  frog, 
which  would  indicate  that  the 
embryo  was  preformed  in  the 
egg  cell,  or  at  least  that  each 
part  of  the  egg  cell  had  its  fate 
predetermim^d,  ho  that  the  loss 
of  part  of  the  egg  would  produce 
a  loss  of  a  definite  part  of  the 
embryo. 

But  in  the  hands  of  other 
investigators  dia  metrically  op- 
posed results  were  got.  Hertwig  managed  to  separate  entirely 
the  two  first  cleavage  cells  and  got  from  each  of  these  half 
eggs  a  complete  embryo  but  of  dwarfed  size,  which  would 
indicate  that  any  part  of  the  egg  stuff  is  able  to  produce  any 
part  of  the  embryo.  Other  investigators  have  succeeded  in 
separating  blastomeres  of  later  cleavage  stages,  and  have 
variously  got  either  miniature  but  complete  embryos  from 
these  fractional  egg  parts,  or  on  the  other  hand  parts  of  embryos 
representing  apparently  the  predetermined  developmental 
fate  of  the  various  parts  of  the  egg.  To  hst  briefly  a  few  of 
these  cases,  we  may  refer  to  the  development  of  partial  embryos 
from  separated  (2-16  cell  stage)  blastomeres  of  various  Cten- 
ophora,  and  the  similar  results  with  the  molluscs  Patella,  Den- 
lalium,  and  Ilyanassa:  to  the  production  of  defective  larvse  by 
the  mutilated  eggs  of  Beroe,  also  of  ascidians  and  of  Echinus: 
to  Driesch's  distinction  between  ectoderm  and  endoderm  after 


'n.x\\' 


Fig.  158. — Lithium  larva  of  the  sea 
urchrn,  Spharccliinus  granularis: 
A,  Elongated  blastula;  B,  evagi- 
nated  gastru'a.     (After  Herbst.) 


FACTORS    IX    ONTOGENY 


279 


the  first  cleavage  of  Symipta,  and  the  cell  lineage  studies  of  zur 
Strassen  on  the  eggs  of  Ascaris  in  wliicli  it  was  shown  that  a 
definite  status  of  outcome  for  each  Ijlastomere  was  determined 
after  successive  early  cleavages.     All  these  results  seem  to  be 


Fig,  159. — A,  Normal  gastrula  of  sea  urchin,  Echinus  microluberculatus;  B.  gastrula  of 
sea  urchin,  Sphd-rechinus  granularis,  from  a  Uthium  culture.      (After  Herbst.) 

good  evidence  for  preformation,  that  is,  for  a  predetermination 
of  the  role  each  part  of  the  egg  cell  is  to  play  in  develo})ment. 
Indeed,  Wilson  is  convinced  that  an  obvious  structural  differ- 
entiation (bands,  zones,  delimited  regions)  can  be  seen  in  the 
undeveloped  eggs  of  numerous  animals,  a  differentiation  corre- 
sponding to  structural  di- 
vergence in  development. 

On  the  other  hand,  nu- 
merous results  of  experi- 
ment speak  just  as  loudly 
against  preformation  or  pre- 
determination. Such  are 
Herlitzka's  half-sized  Triton 
embryos  from  the  two  sepa- 
rated   first    cleavage    cells, 

Driesch's  two  half-sized  and  four  quarter-sized  sea-urchin  j)hitei 
from  tlie  cells  of  the  first  and  second  cleavages,  respectively, 
his  eight  and  sixteen  small  gastruhe,  and  thirty-two  tiny  bias- 
tuhie  from  the  separate  blast omeres  of  the  third,  fourth,  and 
lifth  cleavages  respectively;  also  Zoya's  medusa  embryos  from 


Fig.  160. — .\bnormal  larval  stages  of  the  soa 
urchin,  Spharechinus  granularis,  produced 
by  heat.     (After  Driesch.) 


280 


EVOLUTION   AND   ANIMAL   LIFE 


Fig.  161. — A,  Lateral  view  of  pluteus  larva  of 
Echinus;  B,  lateral  view  of  pluteus  larva  of 
Sph,(cr echinus;  C,  hybrid  pluteus  of  the  female 
Sphcerechinus  and  male  Echinus.  (After  Boveri.) 


separated  blastomeres  of  the  two,  four,  eight,  and  even  sixteen- 

cell  stages  of  developing  hydro-medusa  eggs.     Loeb  was  able 

to  effect  the  bursting  of 

/\   jf^  -^ ^^_^  ^  ^^       the   membrane   of    sea- 

urchin  eggs  and  the  con- 
sequent partial  escape 
or  protrusion  of  parts  of 
the  egg  plasm  forming 
so  -  called  extra  -  ovates. 
Each  of  these  extra- 
ovates  began  develop- 
ment as  a  distinct  blas- 
tula,  the  remainder  of 
the  egg  forming  another 
blastula  (Fig.  163). 
Thus  we  see  that  experimental  work  has,  so  far,  not  afforded 

a  positive  answer  to  the  general  query  proposed  by  the  pre- 
formation versus  epigen- 

esis    problem.     But    at 

the    same    time    it     is 

obvious  that  the  results 

of  the  experimental 

method  are  of  extraor- 
dinary interest   and    of 

brilliant  promise.   What 

seems  to  be  revealed  so 

far,  is  that  the  animal 

egg     is     certainly    not 

rigidly  preformed;  that 

there    is    no     absolute 

predetermination  of  the 

fate  in  development  of 

each    part    of    the   egg 

stuff.      But    that    nor- 
mally in   most   eggs   a 

given   part   of   the  egg 

does  have  a  prospective 

definitive  fate,  bo  that 

one-half  of  the  egg  may 

be  looked  on  as  corresponding  to  one  particular  half  of  the 

future  organism.  However,  the  actual  potentiality  of  any  part 


Fig.  162. — Cleavage  of  Echinus  eggs  iix  water  free 
from  calcium.  Note  that  the  cleav^age  cells  tenc^ 
to  gep^rate  entirely.     (After  Perbst.^ 


FACTORS  IN   ONTOGENY 


281 


of  the  egg  is  not  limited  ])y  its  prospective  fate.  If  accident 
in  nature  or  ruthless  handling  in  the  experimenter's  labora- 
tory destroy  or  remove  part  of  the  egg,  the  remainder  has  a 
power  of  regulation  which  is  in  some  respects  the  highest 
and  most  important  kind  of  organic  adaptation  that  we  know. 

The  same  data  derived  from  the 
experimental  study  of  development,  to- 
gether with  data  got  from  the  experi- 
mental study  of  mature  and  even 
senescent  stages  of  various  organisms, 
constitute  our  chief  evidence  touching 
the  problem  of  mechanism  versus  vi- 
talism. This  problem  may  be  posed  in 
question  form  as  follows:  In  how  far 
can  so-called  vital  phenomena  be  ana- 
lyzed into  physicochemical,  or  mechan- 
ical phenomena?  Is  life  simply  an  in- 
teraction, very  complex  to  be  sure,  and 
so  far  largely  unanalyzed  and  hence  not 
directly  referable  to  specific  physico- 
chemical  causes,  between  substances  of 
particular  chemical  and  physical  struc- 
ture and  those  familiar  forms  of  energy 
known  to  us  in  the  physicochemical 
Vv'orld,  or  is  it  the  result  or  manifestation 
of  an  extra  physicochemical  force  and 
set  of  conditions? 

.When  the  sunflower  bends  its  face 
always  toward  the  sun,  we  do  not  at- 
tribute this  behavior  either  to  the  in- 
telhgence  or  the  instinct  of  the  plant. 
But  when  young  spiderlings  or  moth 
caterpillars  or  green  aphids  just  from 
the  egg  move  ^^•ith  one  accord   toward 

the  light  side  of  the  glass  jar,  we  do  attribute  this  behavior  to 
animal  instinct  or  to  the  exercise  of  a  preference  or  choice. 
When  iron  filings  rush  toward  a  magnet  l)rought  sufhciently 
near  them,  we  have  on  our  tongues'  end  the  suflicient  explana- 
tion of  this  behavior  in  the  single  word  "magnetism."  Now 
the  biological  mechanist,  observing  that  in  all  these  cases 
there  is  a  certain  apparent  definite  relation  between  a  cause 


Fig.  163.  —  Extra  -  ovates 
from  the  eggs  of  the  sea 
urchin,  Arbacia.  By  di- 
luting the  sea  water  the 
osmotic  pressure  bursts 
the  egg  membranes  so 
that  part  of  the  egg  plasm 
issues  and  forms  an  ex- 
tra-ovate.    (After  Loeb.) 


282 


EVOLUTION  AND  ANIMAL  LIFE 


and  an  effect,  presumes 
to  say  that  all  these 
phenomena  may  be 
much  more  nearly  of 
the  same  sort  than  we 
are  accustomed  to  con- 
sider them  to  be.  The 
biological  mechanists 
believe,  in  a  word,  that 
all  vital  phenomena 
will  in  last  analysis 
prove  to  be  truly  phys- 
icochemical  phenom- 
ena; that  organisms 
show  in  their  reactions 
no  new  forces  or  prin- 
ciples, but  that  their 
behavior  is  only  an  im- 
mensely complex  interplay  of  the  same  forces  and  activities 
already  known  to  us  in  the  inorganic  world. 

And  their  belief  is  not  wholly  without  some  basis  of  observed 
or  experimentally  proved  fact.  Many  of  the  simpler  so-called 
vital  phenomena,  especially  the  movements  of  the   simplest 


Fig.  164. — Regeneration  in  Hydra  viridis:   A,  Nor- 
mal hydra  (lines  show  where  piece  was  cut  out)  ; 

B,  1-4,  changes  in  a  piece  of  A  as  seen  from  side ; 

C,  1-4,  same  as  seen  from  end  ;   D,  E,   F,  later 
changes  in  same  piece.      (After    Morgan.) 


J 

m 

Fig.  165. — Regeneration  of  Stentor  cwruleus:  A,  Cut  in  three  pieces;  B,  row  showing 
regeneration  of  the  anterior  piece  ;  C,  regeneration  of  middle  piece  ;  D,  that  of 
posterior  piece.      (After  Morgan.) 


FACTORS  IN'    ONTOGENY 


283 


and  even  the  inore  complex  animals,  have  been  shcvv'n  to 
be  suggestively  like  motion  reactions  in  inorganic  nature.  The 
mechanists  analyze  many  of  the  so-called  instinctive  perform- 
ances of  animals  into  rigorous  taxic  and  tro])ic  reactions  to 
specific  external  influences  or  .'.timuli.     Chemotaxis,  phototaxis, 


t'lG.  166.-  -Regeneration  in  nature  of  starfish,  Linckia.  The  regenerated  specimens 
rihown  in  the  figure  were  collected  as  living  animals  on  the  coral  reefs  of  Samoa. 
These  specimens  show  the  great  capacity  for  regeneration  pos- essed  by  this  star- 
fish a  portion  of  an  arm  being  capable  of  regenerating  the  dis';  and  all  the  other 
arms. 

and  oxygenotaxis,  heliotropism,  geotropism,  thigmotro])ism, 
etc.,  are  the  names  applied  to  the  growth  or  motion  reactions 
of  organisms  or  their  ])arts,  conditioned  by  such  external 
stimuli  01  cmtrol-influences  as  light,  gravitation,  contact,  the 
piesence  vi  oxygon  or  of  various  other  chemical  substances. 
And  an  account  of  the  ingenious  experimentation  which  has 


284 


EVOLUTION  AND  ANIMAL  LIFE 


been  done  to  test  the  truth  of  the  mechanical  assumptions 
is  a  fascinating  chapter  in  the  history  of  modern  biological 
work. 

In  sum  we  may  say  that  there  has  been  in  recent  years  a 
real  advance  on  a  basis  of  experimental  work,  in  the  analysis 
of  many  vital  phenomena  long  considered  mysterious,  or  at 
least  too  complex  for  human  understanding,  into  simpler 
components.     And  that  these  components  are  in  many  cases 

no  other  than  reac- 
tions and  motions 
familiar  to  us  in  in- 
organic nature.  On 
the  other  hand  it 
must  be  said  that 
this  advance,  in  the 
face  of  the  immense 
problem  presented 
by  vital  reactions — 
that  is,  the  behavior 
of  organisms — is  very 
small.  With  all  our 
heart  we  should  wel- 
come all  attempts  to 
do  awav  with  ideas 
of  mysticism  in  con- 
nection with  biologi- 
cal phenomena ;  the 
mechanists  should 
have  our  strong  sym- 
pathy and  our  willing 
support,  but  to  join 
the  more  radical  of 
them  in  their  claim 
that  the  life  mystery 
is  already  solved  in  terms  of  physics  and  chemistry,  that  there 
is  no  longer  any  vital  problem,  would  be  to  surrender  our 
judgment  to  our  inchnation. 

Any  discussion,  however  brief,  of  experimental  work  in 
biology  should  include  a  reference,  at  least,  to  the  striking  and 
suggestive  results  that  have  been  obtained  by  the  application 
of  the  experimental  method  to  the  investigation  of  the  problems 


Fig.  167. — Regeneration  of  the  earthworm  :  A,  Nor- 
mal worm  ;  B-F,  anterior  ends  of  worms  which,  after 
the  removal  of  one  two,  three,  four,  and  five  seg- 
ments, have  regenerated  the  same  number ;  G,  an- 
terior third  cut  off,  only  five  head  segments  regener- 
ated ;  H,  worm  cut  in  two  in  middle,  a  head-end  of 
five  segments  regenerated ;  I,  worm  cut  in  two  be- 
hind the  middle,  a  heteromorphic  tail  regenerated  at 
anterior  end.    (After  Morgan.) 


FACTORS   IN   ONTOGENY 


285 


X^ 


of  fertilization  and  partlienogcnesis.  Jacques  Loeb  has  been 
the  most  active  worker  in  this  hne  and  his  results  are  of  ex- 
treme interest.  He  has,  by  various  physical  or  chemical  treat- 
ment of  the  unfertilized  eggs  of  various  animals,  particularly 
certain  Echinoderms,  worms  and  fishes,  stimulated  these  eggs 
to  begin  development,  which  development  proceeds  either  nor- 
mally or  in  some  degree  abnormally  along  the  usual  path  reg- 
ularly followed  by  the  species.  But  in  all  cases  this  develop- 
ment falls  short  of  completion  and  in  many  cases  the  death  of 
the  embryo  occurs  at  a  very  early  stage.  Other  investigators 
have  similarly  induced  a  de- 
velopment in  parthenogenetic 
eggs  of  animal  species  in 
which  parthenogenetic  devel- 
opment does  not  occur  nat- 
urally, or  at  least  is  very  rare. 
The  significance  of  these 
results  is  by  no  means  wholly 
clear.  Nor  do  the  investiga- 
tors who  have  done  the  work 
agree  among  themselves  as  to 
the  interpretation  of  the  re- 
sults. Loeb  first  inclined  to 
the  belief  that  the  stimuli 
which  incited  the  unfertilized 
egg  to  development  were 
physical,  osmotic  changes  be- 
ing looked  on  as  perhaps  the 
immediate  stimulus.  At  pres- 
ent he  seems  inclined  to  at- 
tribute the  stimuli  rather  to 

the  chemical  character  of  the  media  which  seem  to  incite 
the  parthenogenetic  development.  In  either  case  the  physi- 
cochemical  stimulus  is  considered  to  be  a  substitute  for  the 
spermatozoid.  That  it  is  a  substitute  in  some  degree,  is  obvi- 
ous; that  it  is  a  complete  substitute  for  it,  seems  e(]ually 
obviously  not  true.  The  embryos  develoi")ed  by  artificial  pur- 
theogenesis  lack  at  least  two  fundamentally  important  attri- 
butes which  tlie  young  of  bisexual  jiarentage  possess;  namely, 
vigor  and  the  hcTcdity  of  tlu'  father.  The  lack  of  vigor  is 
shown  by  their  death  before  maturity;  and  the  chromosomes 


Fig.  168. — Regeneration  of  the  flatworm, 
Planaria  lu(}iibris:  A,  shows  by  dotted 
line  where  the  worm  was  cut  in  two  length- 
wise ;  B,  C,  D,  show  how  a  half  that  was 
fed  regenerated  ;  E,  F,  G,  show  how  an 
unfed  half  regenerated.    (After  Morgan.) 


286 


EVOLUTION   AND   ANIMAL   LIFE 


or  other  nuclear  stuff  that  is  the  actual  carrier  of  the  paterPxal 
heredity  are  of  course  actually  wanting. 

Another  phenomenon  or  group  of  phenomena;  also  of  nmch 
special  interest  and  suggestiveness  to  students  of  develop- 
ment, to  which  the  experimental  method  has  been  successfully 
apphed;  is  that  known  as  "regeneration.''  The  familiar  repro- 
duction or  growth  of 
new  plants  from  cut- 
tings or  buds  is  par- 
alleled in  tho  animal 
world  by  numerous 
similar  cases  less  fa- 
miliar but  neverthe- 
less long  known  by 
naturalists.  In  1740, 
Abbe  Trembley  made 
a  number  of  curious 
experiments  with  Hy- 
dra, whose  publication 
in  1744  was  the  begin- 
ning of  our  knowledge 
of  the  phenomena  of 
regeneration  in  ani- 
mals. If  Hydra,  the 
common  little  brown 
or  green  fresh-water 
polyp,  be  cut  up  into 
many  pieces,  each  of 
these  pieces  has  the 
power  to  grow  into  a 
new  complete  Hydra 
body  (Fig.  164).  We  know  now  that  numerous  other  animals 
have  also  this  radical  capacity  for  regeneration.  Certain  pro- 
tozoans, hydroids,  planarian  worms,  starfishes,  etc.,  can  re- 
generate as  freely  or  nearly  so  as  Hydra  (Figs.  165-172).  And 
many  other  animals  representing  almost  all  the  great  groups  of 
the  animaf  kingdom  possess  in  some  degree,  at  least,  the  power 
of  regeneration.  Some  can  regenerate  only  lost  or  cut  append- 
ages, others  even  less  fundamental  parts  of  the  body;  some 
can  regenerate  only  in  their  immature  stages ;  others  only  in 
the  earliest  embryonic  stages.     But  regeneration  and  "regula- 


FiG.  169. — Regeneration  of  the  tail  and  limbs  of 
the  lizards,  Lacerta  agilis  and  Triton  custatus : 
A,  Lacerta,  new  tail  arising  at  place  where  old  tail 
was  broken  partly  off;  B,  three-tailed  form,  two 
tails  having  a  common  covering,  all  these  parts 
being  regenerated  after  old  tail  was  cut  off;  C, 
Triton,  additional  leg  produced  by  wounding  femur; 
D,  double  foot  produced  by  tying  thread  over  re- 
generating stump;  E,  F,  G,  regenerated  feet  of 
Triton  after  various  mutilations.    (After  Tornier. ) 


Factors  in  oxtogekv 


287 


tion/'  as  certain  pliases 
of  regeneration  are 
called,  are  the  property, 
in  some  degree  probably, 
of  most  animals. 

The  significance  of 
this  capacity  has  been 
long  recognized  as  of 
much  importance  in  our 
conceptions  of  the  germ 
plasm  character  and  dis- 
position, but  no  general 
agreement  regarding  it 
has  even  yet  been 
reached  by  biologists. 
More  and  better  under- 
stood facts  about  re- 
generation are  needed. 
And  this  need  it  seems 
to  be  the  province  of 
experimental  biology  to 
supply.  By  the  carry- 
ing on  of  ingeniously  planned  and  carefully  controlled  series 

of  experiments  with  re- 
generating animals,  we 
are  acquiring  a  great 
mass  of  important  data, 
and  the  interpretation 
and  generalization  of 
these  data  is  certain  to 
be  accomplished  in  the 
near  future. 

We  have  space  here 
to  call  attention  to  but 
one  of  the  ways  in  which 
an  understanding  of  the 
phenomena  of  regener- 
ation will  throw  light  on 

Fig.   171.  —  ReKeneration  of  the  eye  of   Triton:  one  of   the  fundamental 

A,  Edge  of  iris  with  beginning  lens ;  B,  C,  D,  ■,   -•                .         ,             i 

later  stnges  of  same  ;E.  whole  eyo  with  regcner-  Pl'OblemS    lU    develop- 

atinglens.     (After  Wolff  and  Fischel  )  mcut.       To      tllOSC     biolo- 


FiG.  170. — Regeneration  of  the  flatworm,  Planaria: 
A,  Specimen  cut  in  two  as  far  forward  as  eyes, 
regenerating  two  half-heads  ;  B,  cut  in  two  at 
one  side  of  middle  line,  smaller  piece  having  re- 
generated a  head  ;  C,  cut  partly  in  two,  having 
regenerated  two  heads  in  angle ;  D,  another 
that  produced  only  a  single  head  in  the  angle. 
(After  Morgan.) 


288 


EVOLUTION  AND  ANIMAL  LIFE 


gists  who  believe  with  W'cismann  that  there  is  a  sharp  distinc- 
tion between  the  germ  plasm  and  the  somatic  or  body  plasm, 
and  that  this  germ  plasm  is  limited  to  the  germ  cells  and 
germ-cell  producing  tracts,  the  regeneration  of  a  nearly  whole 
body  or  even  a  considerable  part  of  a  body  from  a  region  which 
does  not  include  a  germ  cell  presents  a  serious  obstacle.     But 

before  this  obstacle 
can  be  considered  as 
one  rendering  the 
germ  plasm  theory 
absolutely  imtenable, 
it  is  necessary  to 
prove  what  the  re- 
generated parts  are 
composed  of.  Are 
they  composed  sim- 
ply of  repeated  simi- 
lar cells,  all  of  one 
tissue  type,  or  do 
they  include  other 
kinds  of  cells  or  tis- 
sues than  those  par- 
ticular kinds  from 
which  the  regener- 
ated part  springs? 
It  is,  of  course,  ad- 
mitted that  many, 
indeed  most  cells  of 
the  body,  can  repro- 
duce other  cells  like  themselves.  Now  is  it  a  fact  that  regen- 
erated parts  are  composed  of  different  kinds  of  cells?  As  a 
matter  of  fact  this  has  been  proved  to  be  so  by  observation 
and  by  experiment.  Numerous  instances  are  knowm  in  which 
body  cells  arising  originally  from  one  germ  layer  have  pro- 
duced in  the  course  of  regeneration  not  only  cells  like  them- 
selves, but  others  which  in  normal  dcA^elopment  could  only 
arise  from  another  germ  layer.  So  it  is  plain  that  the  study 
of  regeneration  has  already  done  much  to  modify  our  former 
conceptions  of  the  factors  and  conditions  of  development. 


Fig.  172. — Regeneration  of  the  blastula  and  gastrulae 
of  sea  urchins;  line  indicates  where  the  blastula  or 
gastrula  was  cut  in  half;  the  smaller  figures  show  re- 
sults of  the  regeneration  of  the  two  halves  of  each. 


CHAPTER  XIV 
PALEONTOLOGY 

This  much  then  we  have  gained,  that  we  may  assert  without, 
hesitation,  that  all  the  more  j^erfect  organic  natures,  such  as  fishes, 
amphibious  animals,  birds,  mammals,  and  man  at  the  head  of  the  list 
were  all  formed  upon  one  original  type  which  varies  only  more  or  less 
in  parts  which  are  none  the  less  permanent,  and  which  still  daily 
changes  and  modifies  its  form  by  propagation. — Goethe  (1796). 

In  a  suggestive  sentence,  Haeckel  speaks  of  our  knowledge 
of  the  line  of  descent  in  the  history  of  any  group  of  animals  or 
plants  as  being  derived  from  "three  ancestral  documents — 
morphology,  embryology,  and  paleontology/' 

Of  these  three,  paleontology  is  at  once  the  most  certain  and 
the  most  incomplete.  Each  fossil  animal  is  a  record,  absolutely 
authentic,  so  far  as  it  goes,  admitting  of  no  doubt  or  question, 
but  for  the  most  part  yielding  only  a  very  little  of  the  truth 
involved  in  its  existence. 

For  no  animal  whatever  is  preserved  as  a  fossil  except  as 
the  result  of  an  unusual  combination  of  circumstances.  Only 
those  parts  which  are  themselves  hard,  calcareous,  silicious,  or 
horny,  with  rare  exceptions,  can  retain  their  form  in  the  rocks, 
and  even  these,  shells,  teeth,  bones,  and  the  like,  are  often 
crushed  or  distorted  so  that  their  actual  form  or  nature  may 
be  open  to  question.  In  addition,  only  the  minutest  fraction 
of  the  sedimentary  rocks  of  the  earth  has  been  laid  bare  by 
artificial  excavation  or  by  natural  erosion,  and  thus  opened 
to  the  inspection  of  man,  and  the  number  of  fossils  actually 
observed  can  be  only  the  most  trivial  fraction  of  i\  fraction  of 
the  organisms  actually  existing  and  preserved. 

With  all  this,  the  hunian  race  has  in  the  past  shown  a 
singular  lack  9t  insight  in  the  interprotfition  of  animal  remains 

2S9 


290  EVOLUTION  AND  ANIMAL  LIFE 

found  in  the  stone.  As  Lyell  has  graphically  shown,  it  took 
one  hundred  and  fifty  years  of  dispute  and  argument  to  persuade 
even  learned  men  that  shells  and  teeth  in  the  rocks  were  actual 
remains  of  actual  animals,  and  another  hundred  and  fifty  years 
to  demonstrate  that  the  shell-bearing  rocks  were  not  masses 
of  debris  from  Noah's  flood.  Nothing  in  the  history  of  science 
is  more  tedious  than  the  arguments  directed  against  the  first 
students  of  fossils,  to  show  that  these  structures  were  mere 
sports  of  nature,  whimsicalities  of  creation,  or  freaks  developed 
in  the  fatty  matter  {materia  pinguid)  of  the  earth  by  the  en- 
tangling influence  of  the  revolving  stars. 

Notwithstanding  all  these  defects  in  material,  and  this 
stupidity  of  theory,  the  study  of  fossils  has  still  gone  on,  and 
by  its  means  we  are  able  to  delineate  with  large  certainty  the 
line  of  evolution  of  most  groups  of  animals,  and  the  nature  of 
faunal  relations  in  the  different  periods  of  geological  time. 
If  we  had  not  already  a  theory  of  evolution  by  derivation  of 
forms,  we  should  be  obliged  to  invent  one  in  face  of  the  facts  of 
paleontology.  In  Huxley's  words,  "fossils  are  only  animals 
and  plants  which  have  been  dead  rather  longer  than  those 
which  died  yesterday.'' 

Fossils  are  either  actual  remains  of  bones  or  other  parts 
preserved  intact  in  soil  or  rocks,  or  else,  and  more  commonly, 
parts  of  the  animals  which  have  been  turned  into  stone,  or  of 
which  stony  casts  have  been  made.  All  such  remains  buried 
by  natural  causes  are  called  fossils.  The  process  by  which 
they  are  sometimes  changed  from  animal  substance  into  stone 
is  called  petrifaction. 

Fossils  may  be  of  three  kinds.  In  the  case  of  recently 
extinct  animals,  bones  or  other  parts  of  the  body  may  become 
buried  in  the  soil  and  lie  there  for  a  long  time  without  any 
change  of  organic  into  inorganic  matter.  Thus  fossil  insects 
are  found  with  the  bodies  preserved  intact  in  amber,  a  fossil 
resin  from  some  ancient  and  extinct  pine  tree.  Over  eight 
hundred  species  of  extinct  insects  are  known  from  amber 
fossils.  The  bones  of  the  earliest  members  of  the  elephant 
family,  the  teeth  of  extinct  sharks,  the  shells  of  extinct  mollusks 
and  fragments  of  buried  logs,  are  also  often  found  intact,  still 
composed  of  their  original  matter. 

In  the  second  kind  of  fossils  the  original  or  organic  matter 
is  gone,  the  organic  form  and  organic  structure  being  preserved 


PALEONTOLOGY 


^Sl 


Fig.  173. — Remains  of  Dimorphudon  from  tlu;  Lias  of  Lyme  Hfj^is,  showing  skull,  neck, 
and  hack,  and  some  of  the  bones  of  (he  skeleton.  (After  ISeeley,  from  a  slab  in  the 
British  Museum.) 


292  EVOLUTION  AND  ANIMAL  LIFE 

in  mineral  matter.  That  is,  the  organic  matter  has  been 
slowly  and  exactly  replaced  by  mineral.  As  each  particle  of 
organic  substance  passed  away  by  decay,  its  place  was  taken 
by  a  particle  of  mineral  matter.  Such  fossils  are  called  petri- 
factions. This  is  beautifully  shown  in  the  case  of  petrified 
wood.  We  can  cut  and  grind  thin  a  bit  of  petrified  wood,  and 
see  in  it,  with  a  microscope,  the  exact  details  of  its  original 
fine  cellular  structure.  This  substituted  mineral  matter  may 
be  one  of  several  minerals,  but  usually  it  is  silica  (quartz)  or 
carbonate  of  lime  (limestone)  or  sulphide  of  iron  (iron  pjTites). 
In  the  case  of  animal  parts  which  were  originally  partly  organic 
and  partly  inorganic,  as  bones  and  teeth  and  shells,  often  only 
the  organic  matter  is  replaced  by  the  petrifying  mineral, 
although  sometimes  the  old  inorganic  matter  is  also  replaced. 
Finally,  sometimes  the  organic  matter  and  organic  structure 
are  both  lost,  only  the  original  outline  of  form  of  the  whole 
part  being  retained.  This  occurs  when  the  organic  matter 
imbedded  in  mud  and  cla}^  decays  away,  leaving  a  hollow 
which  is  filled  up  by  some  mineral  different  from  the  matrix. 
In  this  case  the  fossil  is  simply  a  cast  of  the  original  organic 
remains. 

Some  traces  even  of  the  finest  organisms  occasionally 
appear. 

"Conditions  have  sometimes  permitted  even  the  most  delicate 
structures,  such  as  insects'  wings  and  the  impressions  of  jellyfishes 
to  become  retained  in  the  soft  mud,  which  afterwards  became  solidi- 
fied. Localities  famous  the  world  over  for  the  beauty  and  delicacy 
of  their  fossil  remains  are  the  lithographic  "stone  quarries  of  Bavaria 
and  certain  beds  in  France  '^  (Eastman). 

These  deposits  were  perhaps  formed  in  the  clear,  quiet  waters 
of  a  coral  lagoon. 

Examination  and  study  of  the  rocks  of  the  earth  reveal  the 
fact  that  fossils,  or  the  remains  of  animals  and  plants,  are 
found  in  certain  kinds  of  rocks  only.  They  are  not  found  in 
lava,  because  lava  comes  from  volcanoes  and  rifts  in  the  earth's 
crust,  as  a  red-hot,  viscous  liquid,  which  cools  to  form  a  hard 
rock.  No  animal  or  plant  caught  in  a  lava  stream  will  leave 
any  trace.  Furthermore,  fossils  are  not  found  in  granite,  nor 
in  ores  of  metals,  nor  in  certain  other  of  the  common  rocks. 


PALEONTOLOGY  293 

Many  rocks  are,  like  lava,  of  igneous  origin;  others,  like 
granite,  although  not  originally  in  melted  condition,  have  been 
so  heated  subsequent  to  their  formation,  that  any  traces  of 
animal  or  plant  remains  in  them  have  been  obliterated.  Fossils 
are  found  almost  exclusively  in  rocks  wliich  have  been  formed 
by  the  slow  deposition  in  water  of  sand,  clay,  mud,  or  lime. 
The  sediment  which  is  carried  into  a  lake  or  ocean  by  the 
streams  opening  into  it  sinks  slowly  to  the  bottom  of  the  lake 
or  ocean  and  forms  there  a  layer  which  gradually  hardens  under 
pressure  to  become  rock.  This  is  called  sedimentary  rock,  or 
stratified  rock,  because  it  is  composed  of  sediment,  and  sedi- 
ment always  arranges  itself  in  layers  or  strata.     In  sedimentary 


Fig.  174. — Restoration  of  the  skeleton  of  Dimorphodon  macronyx.    (After  Seeley.) 


or  stratified  rocks  fossils  are  found.  The  commonest  rocks  of 
this  sort  are  limestone,  sandstone,  and  shales.  Limestone  is 
formed  chiefly  of  carbonate  of  lime;  sandstone  is  cemented 
sand;  and  shales,  or  slaty  rocks,  are  formed  chiefly  of  clay. 

The  formation  of  sedimentary  rocks  has  been  going  on  since 
land  first  rose  from  the  level  of  the  sea;  for  water  has  always 
been  wearing  away  rock  and  carrying  it  as  sediment  into  rivers, 
and  rivers  have  always  been  canying  the  worn-off  lime  and 
sand  and  clay  downward  to  lakes  and  oceans,  at  the  bottoms 
of  which  the  particles  have  been  piled  up  in  layers  and  have 
formed  new  rock  strata.  But  geologists  have  shown  tliat  in 
the  course  of  the  earth's  history  there  have  been  great  clianges 
in  the  position  and  extent  of  land  and  sea.  Sea  bottoms  have 
been  folded  or  upheaved  to  form  dry  land,  wliile  regions,  once 
land,  have  sunk  and  been  covered  by  lakes  and  seas.  Again, 
through  great  foldings  in  the  cooling  crust  of  the  earth,  which 
20 


204 


EVOLUTION  AND  ANIMAL  LIFE 


resulted  in  depression  at  one  point  and  elevation  at  another, 
land  has  become  ocean  and  ocean  land.  And,  in  the  aln  ost 
unimaginable  period  of  time  which  has  passed  since  the  earth 
first  shrank  from  its  hypothetical  condition  of  nebulous  vapor 
to  be  a  ball  of  land  covered  with  water,  such  changes  have 
occurred  over  and  over  again.  They  have,  however,  mostly 
taken  place  slowly  and  gradually.     The  principal  seat  of  great 


Fig.  175. — Restoration  of  the  skeleton  in  probable  normal  position  of  Dimorphodon 

macronyx.     (After   Seeley.) 


change  is  in  the  regions  of  mountain  chains,  which,  in  most 
cases,  are  simply  the  remains  of  old  folds  or  wrinkles  in  the 
crust  of  the  earth. 

When  an  aquatic  animal  dies,  it  sinks  to  the  bottom  of  the 
lake  or  ocean,  unless,  of  coiu-se,  its  flesh  is  eaten  by  some  other 
animal.  Even  then  its  hard  parts  will  probably  find  their 
way  to  the  bottom.  There  the  remains  will  soon  be  covered 
by  the  always  dropping  sediment.  They  are  on  the  way  to 
become  fossils.  Some  land  animals  also  might,  after  death, 
get  carried  by  a  river  to  the  lake  or  ocean,  and  find  their  way 
to  the  bottom,  where  they,  too,  will  become  fossils,  or  they 
may  die  on  the  banks  of  the  lake  or  ocean  and  their  bodies  may 
get  buried  in  the  soft  mud  of  the  shores.  Or,  again,  they  are 
often  trodden  in  the  mire  about  salt  springs  or  submerged  in 
quicksands.  It  is  obvious  that  aquatic  animals  are  far  more 
Ukely   to   be   preserved   as   fossils   than   land   animals.     This 


PALEONTOLOGY 


295 


inference  js  strikingly  proved  by  fossil  remains.  Of  nil  tlie 
thousands  and  thousands  of  kinds  of  extinct  insects,  mostly 
land  animals,  comparatively  few  si)ecimens  are  known  as  fossils. 
On  the  other  hand,  the  shell-bearing  mollusks  and  crustaceans 
are  represented  in  almost  all  rock  deposits  which  contain  any 
kind  of  fossil  remains. 

It  is  obvious  that  any  portion  of  the  earth's  surface  covered 
by  stratified  rocks  must  have  been  at  some  time  under  water, 
the  l)ottom  of  a  lake  or  ocean.  If  now  this  i)ortion  shows  a 
series  of  layers  or  strata  of  different  kinds  of  sedimentary  rocks, 
it  is  evident  that  it  must  have  been  under  water  several  times, 
or  at  least  under  different  conditions.  It  is  also  evident  that 
fossils  found  in  this  portion  of  the  eartli  will  contain  remains 
of  only  those  animals  which  were  living  at  the  various  times 
this  portion  of  the  earth  was  under  water.  Of  tlie  animals 
which  lived  on  it  when  it  was  land  there  will  be  no  trace, 
except,  possibly,  a  few  land  or  fresh-water  forms,  which  might 
be  swept  into  the  sea  or  might  be  preserved  in  the  mud  of  ponds. 


Fig.  176.— Restoration  of  Dimorphodon  macronyx.     (After  Seeley.) 


That  is,  insteaa  of  finding  in  the  stratified  rocks  of  any  ])ortion 
of  the  earth  remains  of  all  the  animals  which  have  lived  on  that 
portion  since  the  earth  began,  we  shall  find,  at  best,  only  re- 
mains of  a  few  kinds  of  those  animals  which  have  lived  on  this 
portion  of  the  earth  when  it^was  covered  by  the  ocean  or  by  a 
great  lake. 

Thus,  the  great  l)ody  of  fossil  remains  of  animals  reveal  only 
a  broken  and  incomplete  history  of  the  animal  life  of  the  past. 
But  the  record;  so  far  as  it  goes,  is  an  absolutely  truthfu]  one, 


296  EVOLUTION   AND  ANIMAL   LIFE 

and  when  the  many  deposits  of  fossils  in  all  parts  of  the  different 
continents  are  examined  and  compared,  it  is  possible  to  state 
numerous  general  truths  in  regard  to  past  life  and  the  suc- 
cession of  animals  in  time.  The  science  of  extinct  life  is  known, 
as  paleontology. 

The  study  of  paleontology  has  revealed  much  of  the  history 
of  the  earth  and  its  inhabitants  from  the  first  rise  of  the  land 
from  the  sea  till  the  present  era.  This  whole  stretch  of  time 
— how  long  no  one  can  guess — is  divided  into  eras  or  ages ;  these 
ages  usuall}^  into  lesser  divisions  called  periods,  and  the  periods 
into  shorter  lengths  of  time  called  epochs.  Each  epoch  is 
more  or  less  sharply  distinguished  from  every  other  by  the 
different  species  of  animals  and  plants  which  lived  while  its 
rocks  were  being  deposited.  In  the  earth's  crust,  where  it  has 
not  been  distorted  by  foldings  and  breaks,  the  oldest  stratified 
rocks  lie  at  the  bottom  of  the  series,  and  the  newest  at  the  top. 
The  fossils  found  in  the  lowest  or  oldest  rocks  represent,  there- 
fore, the  oldest  or  earliest  animals,  those  in  the  upper  or  newest 
rocks  the  newest  or  latest  animals. 

An  examination  of  a  w^hole  series  of  strata  and  their  fossils 
shows  that  what  we  call  the  most  specialized  or  most  highly 
organized  animals  did  not  exist  in  the  earliest  epochs  of  the 
earth's  history,  but  that  the  animals  of  these  epochs  were  all 
of  the  simpler  or  lower  kinds.  For  example,  in  the  earlier 
stratified  rocks  there  are  no  fossil  remains  of  the  backboned 
or  vertebrate  animals.  When  the  vertebrates  do  appear, 
through  several  geological  epochs  they  are  fishes  only,  members 
of  the  lowest  group  of  backboned  animals.  More  than  this, 
they  represent  generalized  types  of  fishes  w^hich  lack  many  of 
the  special  adaptations  to  marine  life  that  modern  fishes  show. 
For  this  reason  they  bear  a  greater  resemblance  to  the  earlier 
reptiles  than  do  the  fishes  of  to-day;  in  other  words,  they 
were  a  generalized  type,  showing  the  beginnings  of  characters 
of  their  own  and  other  types.  It  is  always  through  general- 
ized types  that  great  classes  of  anim.als  approach  each  other. 

In  a  later  epoch  the  batrachians  or  amphibians  appeared; 
in  a  still  later  period,  the  reptiles;  and  last  of  all,  the  birds  and 
the  mammals,  the  last  being  the  highest  of  the  backboned 
animals.  The  following  table  gives  the  names  and  succession 
of  the  various  geological  periods,  and  indicates  briefly  some 
of  the  kinds  of  animals  living  in  each.    In  each  of  these  di- 


PALEONTOLOGY 


297 


Eras  oh 
Pkriods. 

Ages  or  Systems. 

Animai.8  Especiam.y  Characteristic 
OF  THE  Era  or  A<;e. 

Cenozoic. 

Era  of 
Mammals. 

Quaternary  or  Pleis- 
tocene (age  of  man 
and  insects) 

Tertiary:       Pliocene, 
Miocene,  Eocene. .  .  . 

Man;    mammals,  mostly  of  .spe- 
cies still  li\ing. 

Mannnals  abundant;  belonging  to 
numerous  extinct   families  and 
orders. 

Mesozoic. 

Cretaceous 

Jurassic 

Birdlike  rentiles;  flying  reptiles; 
toothed  bird.s;  first  snakes;  bony 
fishes  abound;  sharks  again 
mmieroiis. 

First  birds;  giant  re])til('s;  ammo- 
nites; clams  and  snails  abun- 
dant. 

First    mammals    (a    marsuj)ial); 

b^rsL  ot 
Reptiles. 

1  riassic 

sharks  reduced   to    few   forms; 
bony  fishes  appear. 

Paleozoic. 

Era  of 

Invertebrates. 

Carboniferous  (age  of 
amphibians) 

Devonian      (age      of 
fishes) 

Silurian  (age  of  inver- 
tebrates)   

Ordovician  or  Lower 
Silurian j 

Cambrian 

'Earliest  of   true  reptiles.     Am- 
phibians;   lung  fishes;    fringe 
<|       fins;  first    crayfishes;    insects 
abundant;   spiders;   fresh-wa- 
ter   mussels. 

'  First  amphibian  -  (froglike   ani- 
mals); sharks;  ostracophores; 

1       first  land  shells  (snails);  mol- 

L      lusks  abundant ;  first  crabs. 
First    truly    terrestrial    or    air- 
breathing    animals;    first    in- 
sects; corals  abimdant;  mailed 
fishes. 

r  First     known      fishes,     ostraco- 

1      phores,  mailed  and  with  carti- 

aginous     skeleton;     brachio- 

pods;  triloi)ites.  mollusks.  etc. 

Invertebrates  only. 

Arehean. 

Algonkian.      Lauren-  1 
tian 

Simple  marine  invertebrates. 

visions  of  geological  time  some  one  cla.'^^s  of  animal.-^  was  espe- 
cially numerous  in  species,  and  was  evidently  the  dominant 
group  of  animals  through  that  period.  Tlie  different  ages  are 
therefore , spoken  of  in  terms  of  the  ])revailing  life.  Thus,  the 
"Silurian  Age"  is  known  as  the  age  or  era  of  invertebrates; 
the  "  Devonian,"  as  the  age  of  fishes.  In  the  same  way  we 
have  the  "Reptihan  Age,"  the  "Mammalian  Age,"  according 


298  EVOLUTION  AND  ANIMAL  LIFE 

to  the  great  class  of  animals  predominating  at  that  time.  Of 
course,  in  each  of  the  later  epochs  there  lived  animals  represent- 
ing the  principal  classes  or  groups  in  all  of  the  preceding  ones, 
as  well  as  the  animals  of  that  particular  group  which  may 
have  first  appeared  in  this  epoch,  or  was  its  dominant  group, 


Fig.  177. — Restoration  of  Dimorphodon  macronyx,  showing  probable  wings. 

(After  Seeley.) 

In  the  study  of  fossils  not  only  is  it  necessary  for  us  to 
consider  the  actual  forms  and  structures  and  the  species  they 
represent,  but  we  should  so  far  as  possible  reconstruct  the  con- 
ditions under  which  the  organisms  were  alive,  and  the  threads 
of  genealogy  which  connect  those  of  one  period  with  those 
which  precede  or  follow  them.  By  such  studies  as  these  we  are 
brought  close  to  a  consideration  of  the  method  of  creation,  and 
to  a  knowledge  not  only  of  the  origin  of  species  but  to  the 
causes  underlying  the  divergence  of  the  great  trunks  of  animal 
and  plant  life. 

"In  youth,"  says  Dr.  A.  S.  Packard,  "the  older  naturalists  of  the 
present  generation  were  taught  the  doctrine  of  creation  by  sudden, 
cataclysmal,  mechanical  creative  acts,  and  those  to  whose  lot  it  fell 
to  come  into  contact  with  the  ultimate  facts  and  principles  of  the  new 
biology  had  to  unlearn  this  view,  and  gradually  to  work  out  a  larger, 
more  profound,  wider  reaching  and  more  j^hilosophic  conception  of 
creation." 

An  early  paleontologist,  Dr.  A.  Gaudry,  utters  these  sug- 
gestive words: 

"We  cannot  refrain  from  looking  with  curious  admiration  upon 
the  innumerable  creatures  that  have  become  preserved  to  us  from 


PALEONTOLOGY  299 

the  earth's  early  days  and  calling  tlioiii  to  life  aj^aiii,  and  in  our  imagina- 
tion we  ask  these  ancient  inhabitants  of  the  earth  whence  they  were 
derived  :  'Speak  to  us  and  say  whether  you  are  isolated  remnants 
disseminated  here  and  there  throughout  the  inmiensity  of  the  ages, 
without  order  more  comprehensible  to  us  than  the  scattering  of  flowers 
over  the  prairie?  Or  are  you  in  verity  linked  one  to  another  so  that 
we  may  yet  be  able  amid  the  diversity  of  nature  to  discover  the  in- 
dications of  a  plan  wherein  the  Infinite  has  stamped  the  impression  of 
His  unity?'  The  unraveling  of  the  ])lan  of  creation — this  is  the  goal 
to  which  our  efforts  now  aspire.  Whatever  our  theories,  as  to  it," 
Gaudry  continues,  "there  is  a  plan.  A  day  will  come  when  the 
paleontologists  will  seize  the  i^lan  which  has  presided  over  the  de- 
velopment of  life." 

This  plan  is  found  in  the  phenomena  of  organic  evolution, 
the  interrelation  of  the  different  factors  or  forces  of  heredity, 
variation,  adaptation,  fecundity,  with  the  conditions  of  isola- 
tion of  forms  and  the  relations  of  environment.  In  the  study 
of  these  details,  we  receive  great  light  from  the  investigation 
of  comparative  structure,  and  the  forces  and  processes  of 
individual  development.  These  are  Haeckel's  ancestral  docu- 
ments of  morphology  and  embryology,  but  all  theory  finds  its 
final  verification  in  its  accord  with  the  facts  of  paleontology, 
the  recorded  evidence  of  succession  in  time. 

Among  the  general  deductions  from  paleontology  are  the 
following : 

The  various  primary  groups  or  branches  of  the  animal 
kingdom  as  well  as  the  principal  classes  are  all  very  old,  most 
of  them,  the  vertebrates  excepted,  appearing  in  the  earliest 
known  fossiliferous  rocks.  It  is,  however,  evident  that  these 
rocks.  Lower  Silurian  or  Ordovician  and  Cambrian,  are  very 
far  from  the  actual  beginning  of  life. 

In  each  group  the  earliest  forms  are  relatively  simj^le, 
unspecialized,  and  as  a  rule  marine.  Many  of  them  are  em- 
br3^onic  types,  that  is,  forms  morphologically  comparable  to 
the  embryos  of  forms  of  later  a})pearance.  To  such  forms, 
the  less  appropriate  term  of  "prophetic  types"  has  been  ap- 
plied. Many  of  the  earher  forms  are  of  synthetic  types, 
that  is,  embracing  characters  distinctive  of  different  diver- 
gent groups.  Such  synthetic  typ(*s,  where  the  resemblances 
are  shown  to   be  indicative  of  real   homologv,  are    now   rc^- 


300  EVOLUTION   AND   ANIMAL   LIFE 

garded  as  indicative  of  the  actual  ancestry,  from  which  the 
later  types  have  diverged. 

The  persistence  of  heredity  is  the  basis  of  the  parallelism 
between  geological  and  embryonic  series.  By  its  influence 
ancestral  traits  are  repeated  in  the  embryo,  even  though  the 
characters  thus  produced  give  way  in  later  development  to 
further  specialization  or  growth  along  other  lines.  This  great 
truth  has  been  stated  in  these  words:  "The  life  history  of  the 
individual  is  an  epitome  of  the  life  history  of  the  group  to 
which  it  belongs. '^  This  statement  is  only  true  when  stated 
very  broadly,  for  there  are  many  exceptions  or  modifications. 
The  embryonic  or  larval  animal  is  subject  to  almost  endless 
secondary  changes  and  adaptations  whenever  these  changes 
are  for  the  advantage  of  the  animal.  In  general,  the  simpler 
the  structure  of  the  animal  and  the  less  varied  its  relations  in 
life,  the  more  perfectly  are  these  ancient  phases  of  heredity 
preserved  in  the  process  of  development.  In  such  case,  the 
more  perfect  is  the  parallelism  between  the  development  of 
the  individual  and  the  succession  of  forms  in  geologic  time. 

It  is  not  always  true  that  the  recent  representatives  of  a 
group  are  higher  in  a  morphological  sense  than  some  or  all  of 
the  earlier  members.  They  are,  however,  in  all  cases  farther 
from  the  original  or  parent  stock.  In  many  groups  there  is  a 
progress,  seemingly  rapid,  toward  a  high  degree  of  specializa- 
tion followed  by  the  disappearance  of  the  highly  organized 
types,  while  forms  of  low  development — sometimes  even  those 
of  primitive  character — may  remain  in  abundance.  The  evolu- 
tion of  the  group  of  Brachiopods  is  an  illustration  of  thi^  The 
group  is  represented  in  the  Lower  vSilurian  by  numerous  genera 
of  simple  structure,  as  Lingula,  Terebratida  and  the  like.  It 
culminates  in  the  Carboniferous  age  with  complex  genera  as 
Spirifer,  Productus,  Orthis,  while  the  modern  representatives 
Lingulella,  Terebrahdina,  Waldheimia,  etc.,  are  little  more  ad- 
vanced than  the  primitive  forms.  Similar  phases  have  charac- 
terized the  appearance,  culmination,  and  relative  extinction 
of  the  trilobites,  the  crinoids,  the  ammonites,  and  other  groups. 
The  total  extinction  of  any  large  group  has  not  usually  taken 
place.  Usually  a  few  species  have  remained,  thus  giving  us  a 
better  clew  to  the  life  history  and  development  of  the  group 
than  we  should  otlierwise  possess. 

One  feature  shown  in  many  groups  of  extinct  animals  has 


PALEONTOLOGY  301 

never  received  accurate  definition  or  interpretation.  The 
group  may  appear  in  a  series  of  relatively  simple  forms,  showing 
affinities  with  some  type  from  which  it  may  have  diverged. 
These  early  genera  will  be  succeeded  in  the  rocks  by  others, 
arranged  progressively  so  as  to  form  a  series  apparently  mov- 
ing in  a  certain  direction.  Each  genus  successively  following 
in  time,  will  perhaps  show  a  greater  and  greater  emphasis  on 
some  one  group  of  characters,  a  greater  and  greater  si^ecializa- 
tion  in  some  one  direction.  Arranging  the  genera  in  series,  it 
looks  as  if  there  were  a  definite  line  of  variation  shown  in  their 
gradual  succession.  These  phenomena  have  been  shown  in 
various  groups  of  reptiles  and  fishes,  and  especially  well  in  the 
evolution  of  the  extinct  order  of  ammonites.  These  animals, 
allied  to  the  living  nautilus,  lived  in  coiled  chaml)ered  shells 
which  gradually  assumed  great  complication  of  form  and  orna- 
mentation. The  extreme  of  this  course  of  evolution  was  fol- 
lowed b}^  corresponding  progreshivc  degeneration.  In  some 
cases,  this  condition  continues  to  the  present  time.  ^lore 
frequently,  the  specialization  along  the  original  lines  continues 
to  a  certain  point,  to  be  followed  by  the  progressive  degenera- 
tion and  perhaps  the  ultimate  loss  of  the  very  same  structures 
in  wiiich  the  high  degree  of  specialization  has  prevailed. 

To  phenomena  of  this  kind,  tlie  term  determinate  varia- 
tion or  orthogenesis  has  been  applied.  This  phrase  seems  to 
involve  the  theory  that  the  evolution  has  gone  forward  toward 
some  predetermined  end,  or  that  in  some  way  only  variations 
leading  toward  this  end  have  existed  or  at  least  have  been 
able  to  maintain  themselves.  It  is  possible,  however,  that  the 
cause  may  be  found  in  the  influence  of  some  phase  of  environ- 
ment, which  directs  the  course  of  natural  selection  continuously 
along  a  certain  line.  A  reversal  of  selection  would  be  naturally 
foUow^ed  by  a  degeneration  of  the  structures  developed  to  a 
point  be3'ond  the  need  of  the  animal. 

It  is  plain  that  much  is  to  be  learned,  especially  in  regard  to 
the  relationships  existing  among  living  animals,  by  a  study  of 
those  of  the  past.  A  comparison  of  certain  of  the  ancient 
reptiles  with  the  long-tailed  Archaoptcryx  (Fig.  178)  and  other 
toothed  birds  shows  that  the  birds  and  reptiles  were  once 
scarcely  distinguishable,  although  now  so  very  different.  Birds 
have  feathers,  reptiles  do  not ;  but  there  is  scarcely  any  other 
permanent    difference.      Fossils  show  a  similar  close  relation 


302 


EVOLUTION  AND  ANIMAL  LIFE 


between  amphibians  and  fishes.  A  study  of  these  ancient 
forms  also  throws  hght  on  many  conditions  of  structure  in 
modern  animals,  otherwise  difficult  to  understand.  An  exam- 
ple of  this  sort  is  found  in  the  sphnt  bones  of  the  modern 
horse  (see  Fig.  179). 

It  is  a  fact  unquestionable  that  a  species  will  change  on  its 
0"svn  grounds  little  by  little  with  the  lapse  of  time  and  the  slow 
alteration  of  conditions  of  selection.  Nations  change,  languages 
change,  customs  change,  nothing  is  secure  against  the  tooth  of 


Fig.  178. — Ancient  bird  with  jointed  tail,  claws  on  wings,  and  teeth  in  jaws,  Archcvop- 
teryx  lithographica,  from  the  Jurassic  rocks  of  Bavaria.  (After  Nicholson  from 
Owen.) 


time.  This  is  in  general  true,  because  with  time,  alteration  of 
environment  takes  place,  events  happen,  there  is  an  alteration 
of  the  stress  of  Hfe  and  with  this  alteration  all  life  may  be  acted 
upon. 

That  time-mutations  in  all  forms  of  life  do  take  place  is 
beyond  -c[uestion,  and  some  have  regarded  these  slow  changes 
as  the  chief  agency  in  the  formation  of  species.  But  the 
current  of  life  does  not  flow  in  straight  lines  nor  in  an  even 
current.  Species  are  torn  apart  by  obstacles,  as  streams  are 
divided  by  rocks,  and  the  rapidity  of  their  formation  is  pro- 
portioned to  the  size  of  the  obstacle  and  the  alternations  it 
produces  in  the  flow  of  life. 

We  have  some  basis  for  the  estimate  of  the  duration  of  a 
species.     When  the  great  glacial  Lake  Bonneville  occupied 


PALEONTOLOGY 


303 


the  basin  of  the  Great  Salt  Lake,  the  same  species  of  fishes 
and  insects  were  found  in  all  its  tributaries.  Now  that  these 
streams  flow  separately  into  a  lifeless  lake,  the  same  species 
of  fishes  occur  in  them  for  the  most  part  without  alteration. 
One  species  of  sucker  {Catoslomus  ardens)  and  one  chub  {Leiicis- 
cus  lineatus)  are  found  unaltered  throughout  this  region  and 
in  the  Upper  Snake  River  (al)ove  Shoshone  Falls),  into  whicli 
Lake  Bonneville  was  once  drained.  Other  species  are  left 
locally  isolated,  but  one  species 
only  (Agosia  adobe),  a  small 
minnow  pf  the  clay  bottoms, 
can  be  shown  to  have  under- 
gone any  alteration.  But  with 
the  tiger  beetles  (Cicindelce) 
a  large  number  of  species 
have  been  produced  by  sepa- 
ration. 

From  the  Bay  of  Panama 
374  species  of  fishes  are  re- 
corded in  the  recent  mono- 
graph of  Gilbert  and  Starks. 
Of  these  species,  204  are  re- 
corded also  from  the  Gulf  of 
California,  while  perhaps  fifty 
others  are  represented  in  tlTe 
more  northern  bay  by  closely 
related  forms.  Comparing  the 
fish  faunas  separated  by  the 
isthmus,  w^e  find  the  closest 
relation  possible  so  far  as 
families  and  genera  are  con- 
cerned. In  this  respect  the  resemblance  is  far  closer  than 
that  between  Panama  and  .Chile,  or  Panama  and  Tahiti,  or 
Panama  and  southern  California.  On  the  Atlantic  side,  simi- 
lar conditions  obtain,  although  the  number  of  genera  and 
species  is  far  greater  (about  1,200  species)  in  the  West  Indies 
than  at  Panama.  This  fact  accords  with  the  much  larger  ex- 
tent of  the  West  Indies,  its  varied  groups  of  islands  isolated 
by  deep  channels,  and  its  near  connection  to  the  faunas  of 
Brazil  and  the  United  States. 

But  it  is  also  noteworthy  that  while  the  families  of  fishes 


Fig.  179. — Diagrams  showing  the  series 
of  changes  in  geological  time  from  a 
horse's  foot  of  four  separate  toes  (/)  to 
one  of  one  toe  and  a  pair  of  splint 
bones  (a);  a-/ represent  the  feet  of  dif- 
ferent horselike  animals  from  modern 
time  backward. 


304  EVOLUTION  AND  ANIMAL  LIFE 

are  almost  identical  on  the  two  shores  of  the  isthmus  of  Panama, 
and  the  great  majority  of  the  genera  also,  yet  the  species  are 
almost  wholly  different. 

Taking  the  enumeration  of  Gilbert  and  Starks,  we  find  that 
cut  of  374  species,  43  are  found  apparently  unchanged  on  both 
sides  of  the  isthmus ;  265  are  represented  on  the  Atlantic  side  by 
closely  related  species — in  most  cases  the  nearest  known  relative 
of  the  Pacific  species — while  64  have  no  near  analogue  in  the 
Atlantic.  Of  the  latter  group,  some  find  their  nearest  relative 
to  the  northward  or  southward  along  the  coast,  and  still  others 
in  the  islands  of  Polynesia. 

The  almost  unanimous  opinion  of  recent  students  of  the 
isthmus  faunas  finds  expression  in  the  following  words  of  Gilbert' 
and  Starks  {"  Fishes  of  Panama  Bay,''  p.  205): 

"The  ichthyological  evidence  is  overwhelmingly  in  favor  of  a 
former  open  communication  between  the  two  oceans,  which  must  have 
become  closed  at  a  period  sufficiently  remote  from  the  present  to 
have  permitted  the  specific  differentiation  of  a  very  large  majority  of 
the  forms  involved.  That  this  differentiation  progressed  at  widely 
varying  rates  in  different  instances,  becomes  at  once  apparent.  A 
small  minority  (43)  of  the  species  (11  per  cent  of  the  species  found  on 
the  Pacific  side;  about  2.5  of  the  combined  fauna)  remain  wholly 
unchanged  so  far  as  we  have  been  able  to  determine  that  point.  A 
larger  number  have  become  distinguished  from  their  representatives 
of  the  opposite  coast  by  minute,  but  not  'trivial'  differences,  which 
are  wholly  constant.  From  such  representative  forms  we  pass  by 
imperceptible  gradation  to  species  much  more  widely  separated,  whose 
immediate  relation  in  the  past  we  cannot  confidently  affirm.  .  .  . 

"It  is  obvious,  however,  that  the  striking  resemblances  between 
the  two  faunas  are  shown  as  well  by  slightly  divergent  as  well  as  by 
identical  species,  and  the  evidence  in  favor  of  interoceanic  connection 
is  not  weakened  by  an  increase  in  the  one  list  at  the  expense  of  the 
other.  All  evidence  concurs  in  fixing  the  date  of  that  connection  at 
some  time  prior  to  the  Pleistocene,  probably  in  the  early  Miocene. 
When  geological  data  shall  be  adequate  definitely  to  determine  that 
date,  it  will  give  us  the  best  known  measure  of  the  rate  of  evolution  in 
fishes." 

From  this  discussion,  it  is  probable  that  even  in  isolation 
some  species  change  very  slowly,  that  with  similar  conditions 


PALEONTOLOGY  305 

the  changes  within  isolated  groups  of  a  species  may  be  parallel, 
and  that  the  specific  changes  in  different  groups  may  progress 
with  very  different  degrees  of  velocity. 

The  earliest  known  vertebrate  remains  are  found  in  rocks  of 
the  Ordovician  age,  approximately  of  the  epoch  known  as 
Trenton,  at  Caiion  City,  in  Colorado.  These  remains  consist 
of  broken  bits  of  bony  shields  of  mailed  fishes  or  fishlike  forms 
known  as  Ostracophores.  With  these  are  fragments  of  scales, 
which  seem  to  belong  to  more  specialized  forms.  It  is  evident 
that  these  remains,  as  well  as  the  remains  of  sharks  which 


Fig.  180. — An  ostracoderm,  Pterichyodes  milleri,  from  the  lower  Devonian  of  Scotland. 
The  jointed  appendage  on  the  head  is  not  a  limb.     (After  Traquair.) 

appear  later  in  the  Upper  Silurian,  by  no  means  reveal  the 
actual  first  existence  of  vertebrates. 

The  sharks  which  appear  in  the  Upper  Silurian,  although 
certainly  primitive,  even  as  compared  with  later  sharks,  are 
very  far  from  the  simplest  even  of  known  vertebrates.  There 
seems  to  be  good  reason  for  the  view  that  the  vertebrate  type  of 
animal,  with  the  nervous  cord  along  the  back  and  the  alimentary 
canal  marked  by  gill  slits,  was  at  first  soft-bodied  and  worm- 
like, in  fact,  derived  from  a  wormlike  ancestry,  and  that,  prior 
to  the  Ordovician  and  Silurian  time,  it  was  devoid  of  hard 
parts.  The  early  sharks  have  teeth,  and  rough  skin,  fins,  and 
sometimes  fin  spines,  all  susceptible  of  preservation  in  the 
rocks,  even  though  the  skeleton  was  soft  and  cartilaginous. 
Tlie  Ostracophores,  some  of  which,  at  least,  seem  to  be  modified 
sharks,  had  no  internal  hard  parts,  but  were  protected  by  an 
external  coat  of  mail,  perhaps  formed  of  coalesccnt  prickles  or 
scales. 

From  the  sharks  were  doubtless  descended  the  group  of 
Fringe-fins  or  Crossopterygians,  which  were  more  distinctly 
fishlike.    From  these,  on  the  one  hand  by  continuous  speciali- 


306 


EVOLUTION   AND   ANIMAL   LIFE 


zation  for  aquatic  life,  the  true  fishes  must  have  been  derived. 
In  the  more  primitive  of  these  the  air  bladder  retains  the  lung- 
like structure  characteristic  of  the  Fringe-fins.  But  in  the 
more  specialized  forms  this  is  reduced  to  a  sac,  at  first  with  an 
open  tube,  then  to  a  closed  sac  without  tube  in  the  adult,  and 
finally  in  very  many  of  the  true  fishes  the  air  sac  is  altogether 
lost.  On  the  other  hand,  in  the  Amphibia,  which  were  prob- 
ably also  derived  from  the  Crossopterygia,  the  air  bladder  is 
more  highly  specialized,  fitting  these  animals  for  Hfe  outside 

the  water,  and  the 
fins  give  place  to 
fingers  and  toes  as 
befitting  a  terres- 
trial habit. 

The  ampliibians 
deposit  their  eggs  in 
damp  places,  and 
the  young  are 
hatched  while  the 
external  gills  are 
still  functional. 

Among  the  rep- 
tiles, which  mark  the  next  stage  of  adaptation  for  terrestrial 
life,  the  gills  are  absorbed  before  the  animal  leaves  the  egg. 
The  reptile  is  therefore  no  longer  confined  to  the  neighbor- 
hood of  the  water  for  purposes  of  reproduction. 

The  bird,  derived  from  the  reptile,  and  at  first  distin- 
guishable solely  by  the  possession  of  feathers,  loses  later 
various  reptilian  traits  and  the  group  becomes  one  inhabit- 
ing the  air. 

From  the  reptiles  again  are  derived  the  lowest  mammals. 
The  Monotremes  of  Australia  lay  eggs  as  reptiles  do,  these,  like 
reptiles^  eggs,  being  covered  with  a  leathery  skin.  The  higher 
mammals  hatch  the  eggs  within  the  body,  nourish  them  with 
milk  and,  in  general,  care  for  them  in  a  degree  unknown  within 
the  class  of  reptiles.  The  traits  of  external  hair,  warm  blood, 
double  circulation  of  the  blood  from  and  to  a  two-chambered 
heart,  and  other  characters  of  the  mammals  become  fixed  with 
time  and  the  group  diverges  into  a  multitude  of  forms  living 
and  extinct,  the  last,  and  on  the  whole  the  most  specialized  of 
the  sories  being  Homo,  the  genvig  of  man, 


Fig.  181. — The  flying  dragon  (Draco).     (After  Seeley.) 


PALEOKTOLOGY 


307 


The  first  traces  of  man  appear  in  the  later  geologic  times 
after  the  end  of  tTie  Tertiary.  Human  bones  have  been  found 
in  caves  together  with  those  of  the  cave-lion,  cave-bear,  antl 
other  extinct  animals.  In  certain  hikes  in  Switzerland  and 
Austria  have  been  found  remains  of  i)eculiar  dwellings,  to- 
gether with  ancient  fishing  hooks  and  a  variety' of  imple- 
ments of  stone  and  bronze.  These  houses  were  \nn\t  on  piles 
in  the  lakes,  and  connected  with  the  shore  by  piers  or  Ijridges. 
The  extinct  race  of  men  who  lived  in  them  is  known  as 
Lake-dwellers.  Relics  of  man,  especially  rough  stone  tools 
and  Hint  arrow  and  axe  heads,  and  skulls  and  other  bones, 


Fig.  182. — Rough  drawing  of  a  mammoth  on  its  own  ivory,  by  a  contemporary  man. 

(After  Le  Conte.) 


have  been  found  under  circumstances  which  indicate  with 
certainty  that  man  has  existed  long  on  the  earth.  But  with 
these  relics  very  few  bones  are  found.  This  has  been  ac- 
counted for  by  supposing  that  man  existed  in  a  few  wander- 
ing tribes  scattered  widely  over  Europe.  In  Java  are  found 
some  ancient  bones  of  manlike  animals  (Pithecanthroptis) ,  dif- 
ferent, however,  from  any  species  or  race  of  men  living  to-day, 
and  showing  traits  which  indicate  a  close  relationship  with  the 
anthropoid  apes. 

The  time  of  historic  man — i.  e.,  the  period  which  has  elapsed 
since  the  history  of  man  can  be  traced  from  carvings  or  buildings 
or  writings  made  by  himself — is  short  indeed  compared  with 
that  of  prehistoric  man.  Barbarous  man  writes  no  liistory 
and  leaves  no  record  save  his  tools  and  his  bones.  Iron  and 
bronze  rust,  bones  decay,  wood  disappears.     Only  stone  im- 


308  EVOLUTION  AND  ANIMAL  LIFE 

plements  remain  to  tell  the  tale  of  primitive  humanity.     These 
give  no  exact  record  of  chronology. 

So  of  the  actual  duration  of  man's  prehistoric  existence  we 
can  make  no  estimate.  Speaking  in  terms  of  the  earth's 
history,  man  is  very  recent,  the  latest  of  all  the  animals.  In 
terms  of  the  history  of  man,  he  is  very  ancient.  The  exact 
records  of  human  history  cover  only  the  smallest  fraction  of 
the  period  of  man's  existence  on  earth. 


CHAPTER  XV 
GEOGRAPHICAL  DISTRIBUTION 

Is  not  the  biological  laboratory  which  leaves  out  the  ocean  and  the 
mountains  and  meadows  a  monstrous  absurdity?  Was  not  the  greatest 
scientific  generalization  of  your  times  reached  independently  by  two 
men  who  were  eminent  in  their  familiarity  with  living  beings  in  their 
homes? — Brooks. 

Under  the  head  of  "Geographical  Distribution"  we  con- 
sider the  facts  of  the  diffusion  of  organisms  over  the  surface 
of  the  earth,  and  the  laws  by  which  this  diffusion  is  governed. 

The  geographical  distribution  of  animals  is  often  known  as 
"  zoogeography. '^  In  physical  geography  we  may  prepare 
maps  of  the  earth  which  shall  bring  into  prominence  the 
physical  features  of  its  surface.  Such  maps  would  show  here 
a  sea,  here  a  plateau,  here  a  range  of  mountains,  there  a  desert, 
a  prairie,  a  peninsula,  or  an  island.  In  political  geography  the 
maps  show  the  physical  features  of  the  earth,  as  related  to  the 
states  or  powers  which  claim  the  allegiance  of  the  people.  In 
zoogeography  the  realms  of  the  earth  are  considered  in  relation 
to  the  types  or  species  of  animals  which  inhabit  them. 

Thus  a  series  of  maps  of  the  United  States  could  be  drawn 
which  would  show  the  gradual  disappearance  of  the  buffalo 
before  the  attacks  of  man.  Another  might  be  drawn  which 
would  show"  the  present  or  past  distribution  of  tlie  }X)lar  bear, 
black  bear,  and  grizzly.  Still  another  might  show  the  original 
range  of  the  wild  hares  or  rabbits  of  the  United  States,  the 
white  rabbit  of  the  Northeast,  the  cottontail  of  the  East  and 
South,  the  jack  rabbit  of  the  j^lains,  the  snowshoe  rabbit  of 
the  Columbia  River,  the  tall  jack  rabbit  of  California,  the  marsh- 
hare  of  the  South  and  the  waterhare  of  the  canebrakes,  and 
that  of  all  their  relatives.  Such  a  map  is  very  instructive,  and 
21      •  309 


810 


EVOLUTION  A.MD  AKIMAL  LIFE 


Fig.  183. — Map  showing  the  distribution  of  the  Canadian  Skipper  butterfly,  Erynnii 
manitoba,  in  the  United  States.  The  butterfly  is  found  in  that  part  of  the  couiitry 
shown  in  the  map.  This  butterfly  is  subarctic  and  subalpine  in  distribution  being 
found  only  far  north  or  on  high  mountains,  the  two  southern  projecting  parts  oi" 
its  range  being  in  the  Rocky  Mountains  and  in  the  Sierra  Ncv;:.da  Mountains.  (After 
Scudder.) 


LEREMA 
-^        ACCIUS 


Fig.  184. — Map  showing  the  distribution  of  the  Clouded  Skipper  butterfly,  Lerema 
accius,  in  the  United  States.  The  butterfly  is  found  in  those  parts  of  the  country 
shown  in  the  map  by  the  shading  marks — the  warm,  moist  Southern  and  Eastern 
parts.     (After  Scudder.) 


GEOGRAPHICi^::.   DISTRIBUTION  311 

it  at  once  raises  a  series  of  questions  as  to  the  reasons  for  eacli 
of  the  facts  in  geographical  distribution,  for  it  is  the  duty  of 
science  to  suppose  that  none  of  these  facts  is  arbitrary  or  mean- 
ingless.    Each  fact  has  some  good  cause  behind  it. 

It  was  this  phase  of  the  sul^ject,  the  relation  of  species  to 
geography,  which  first  attracted  the  attention  of  both  Darwin 
and  Wallace.  Both  these  observers  noticed  that  island  life 
is  neither  strictly  like  nor  unlike  the  life  of  the  nearest  land, 
and  that  the  degree  of  difference  varies  with  the  degree  of 
isolation.  Both  were  led  from  this  fact  to  the  theory  of  deriva- 
tion, and  to  lay  the  greatest  stress  on  the  progressive  modifica- 
tion resulting  from  the  struggle  for  existence. 

In  the  voyage  of  the  Beagle  Darwin  was  brought  in  contact 
with  the  singular  fauna  of  the  Galapagos  Islands,  that  cluster 
of  volcanic  rocks  which  lies  in  the  open  sea  about  six  hundred 
miles  west  of  the  coasts  of  Ecuador  and  Peru.  The  sea  birds 
of  these  islands  are  essentially  the  same  as  those  of  tne  coast  of 
Peru.  So  with  most  of  the  fishes.  We  can  see  how  this  miglit 
well  be,  for  both  sea  birds  and  fishes  can  readily  pass  from  the 
one  region  to  the  other.  But  the  land  birds,  as  well  as  the 
reptiles,  insects,  and  plants,  are  largely  peculiar  to  the  islands. 
Many  of  these  species  are  found  nowhere  else.  But  other 
epecies  very  much  like  them  in  all  respects  are  found,  and  these 
live  along  the  coast  of  Peru.  In  the  Galapagos  Islands,  ac- 
cording to  Darwin's  notes, 

"  there  are  twenty-six  land  birds ;  of  these,  twenty-one,  or  perhaps 
twenty-three,  are  ranked  as  distinct  species,  and  would  be  commonly 
assumed  to  have  been  here  created;  yet  the  close  affinity  of  the  most 
of  these  birds  to  American  species  is  manifest  in  every  character,  in 
their  habits,  gestures,  and  tones  of  voice.  So  it  is  with  the  other 
animals  and  with  a  large  proportion  of  the  plants. 

"...  The  naturalist,  looking  at  the  inhabitants  of  these  vol- 
canic islands  in  the  Pacific,  feels  that  he  is  standing  on  American  land," 

This  question  naturally  arises:  If  these  species  have  been 
created  as  we  find  them  on  the  Galapagos,  why  is  it  that  they 
should  all  be  very  similar  in  type  to  other  animals,  living  irnder 
wholly  different  conditions,  but  on  the  coast  not  far  away? 
And,  again,  why  are  the  animals  and  plants  of  another  cluster 
of  volcanic  islands — the  Cape  Verde  Islands — similarly  related 


312  EVOLUTION  AND  ANIMAL  LIFE 

to  those  of  the  neighboring  coast  of  Africa,  and  wholly  unlike 
those  of  the  Galapagos?  If  the  animals  were  created  to  match 
their  conditions  of  life,  then  those  of  the  Galapagos  should  be 
like  those  of  Cape  Verde,  the  two  archipelagoes  being  extremely 
alike  in  soil,  climate,  and  physical  surroundings.  If  the  species 
on  the  islands  are  products  of  separate  acts  of  creation,  what  is 
there  in  the  nearness  of  the  coasts  of  Africa  or  Peru  to  influence 
the  act  of  creation  so  as  to  cause  the  island  species  to  be,  as  it 
were,  echoes  of  those  on  shore? 

If,  on  the  other  hand,  we  should  adopt  the  obvious  sug- 
gestion that  both  these  clusters  of  islands  have  been  colonized 
by  immigrants  from  the  mainland,  the  fact  of  uniformity  of 
type  is  accounted  for,  but  what  of  the  difference  of  species? 
If  the  change  of  conditions  from  continent  to  island  causes 
such  great  and  permanent  changes  as  to  form  new  species  from 
the  old,  why  may  not  like  changes  take  place  on  the  mainlands 
as  well  as  on  the  islands?  And  if  possible  on  the  mainland  of 
South  America,  what  evidence  have  we  that  species  are  perma- 
nent anywhere?  May  they  not  be  constantly  changing?  May 
what  we  now  consider  as  distinct  species  be  only  the  present 
phase  in  the  changing  history  of  the  series  of  forms  which  con- 
stitute the  species? 

The  studies  of  island  life  can  lead  but  to  one  conclusion: 
These  volcanic  islands  rose  from  the  sea  destitute  of  land  life. 
They  were  settled  by  the  waifs  of  wind  and  of  storm,  birds 
blown  from  the  shore  bv  trade  winds,  lizards  and  insects  carried 
on  drift  logs  and  floating  vegetation.  Of  these  waifs  few  came 
perhaps  in  any  one  year,  and  few,  perhaps,  of  those  who  came 
made  the  islands  their  home;  yet,  as  the  centuries  passed  on, 
suitable  inhabitants  were  found.  That  this  is  not  fancy  we 
know,  for  we  have  the  knowledge  of  specific  examples  of  the 
very  same  sort.  We  know  how  many  animals  are  carried  from 
their  natural  homes.  One  example  of  this  may  be  seen  by 
those  who  have  approached  our  eastern  shores  by  sea  in  the 
face  of  a  storm.  Many  land  birds — sparrows,  warblers,  chick- 
adees, and  even  woodpeckers — are  carried  out  b}-  the  wind, 
a  few  falling  exhausted  on  the  decks  of  ships,  a  few  others  fall- 
ing on  offshore  islands,  like  the  Bermudas,  the  remainder 
drowning  in  the  sea. 

Of  the  immigrants  to  the  Galapagos  the  majority  doubtless 
die  and  leave  no  sign.     A  few  remain,  multiply,  and  take 


GEOGRAPHICAL  DISTRIBUTION 


313 


U      I 

»  -3 
>  O 
O     C 


o  . 

c 

S  '- 

O  ■/, 


^  .2 


0^    a 


OS      33 

1'^ 


-'"   »C1  "~ 


o 

4;     t 


c  2 

O  5 

00 


2  S 

33  t« 

~  -3 

►-I  O 

^-^  w 

=3  5 


-   ^     M 


r^ 


z"  :•  -2  § 


— 

-B 

a 

St 

««* 

£-. 

»— 1 
C 

b 

T3 

CQ 

hC 

00 

C 

C 

• 

*^^ 

0 

^ 

05 

u 

f. 

'a 
O 

N 

_x 

C 

u 

c 

»-^ 

.5 

_rt 

"3 

C 

M 

— 

v 

C 

e3 

>i 

^ 

-S 

s 

••-* 

•^- 

L. 

J  '"^ 

2 

c 

> 

1 

< 

*-> 

b 

c 

ffl 

T. 

a 

"C 

5 

^ 

•2 

r. 

c 

-r 

C     -     X     t 


X  _= 


of 

00 


Si-. 


^   I   c   a   ci 

3 
o 
C 

I 


fc     ^ 


314  EVOLUTION  AND  ANIMAL  LIFE 

possession,  and  their  descendants  are  thus  native  to  the 
islands.  But,  isolated  froni  the  great  mass  of  their  species 
and  bred  under  new  surroundings,  these  island  birds  come  to 
differ  from  their  parents,  and  still  more  from  the  great  mass 
of  the  land  species  of  which  their  ancestors  were  members. 
Separated  from  these,  their  individuality  would  manifest  itself. 
They  would  assume  with  new  environment  new  friends,  new 
foes,  new  conditions.  They  would  develop  qualities  peculiar 
to  themselves — qualities  intensified  by  isolation.  Local  pecu- 
liaiities  disappear  with  wide  association,  and  are  intensified 
when  individuals  of  similar  peculiarities  are  kept  together. 
Should  later  migrations  of  the  original  species  come  to  the 
islands,  the  individuals  surviving  would  in  time  form  new 
species,  or,  more  likely,  mixing  with  the  mass  of  those  already 
arrived,  their  special  characters  would  be  lost  in  those  of  the 
majority. 

The  Galapagos,  first  studied  by  Darwin,  serve  to  us  only  as 
an  illustration.  The  same  problems  come  up,  in  one  guise  or 
another,  in  all  questions  of  geographical  distribution,  whether 
on  continent  or  island.  The  relation  of  the  fauna  of  one  region 
to  that  of  another  depends  on  the  ease  with  whifsh  barriers  may 
be  crossed.  Distinctness  is  in  direct  proportion  to  isolation. 
What  is  true  in  this  regard  of  the  fauna  of  any  region  as  a  whole, 
is  likewise  true  of  any  of  its  individual  species.  The  degree  of 
resemblance  among  individuals  is  in  direct  proportion  to  the 
freedom  of  their  movements,  and  variations  within  what  we 
call  specific  limits  is  again  proportionate  to  the  barriers  which 
prevent  equal  and  perfect  diffusion. 

The  laws  governing  the  distribution  of  animals  are  reducible 
to  three  very  simple  propositions.  Every  species  of  animal  is 
found  in  every  part  of  the  earth  having  conditions  suitable  for 
its  maintenance  unless: 

(a)  Its  individuals  have  been  unable  to  reach  this  region^ 
through  barriers  of  some  sort;  or, 

(6)  Having  reached  it,  the  species  is  unable  to  maintain 
itself,  through  lack  of  capacity  for  adaptation,  through  severity 
of  competition  with  other  forms,  or  through  destructive  con- 
dition of  environment ;  or, 

(c)  Having  entered  ana  maintained  itself,  it  has  become 
so  altered  in  the  process  of  adaptation  as  to  become  a  species 
distinct  from  the  original  type. 


GEOGRAPHICAL   DISTRIBUTION  315 

As  examples  of  the  first  class  we  may  take  the  absence  of 
kingbirds  or  meadow  larks  or  coyotes  in  Europe,  the  absence 
of  the  Hon  and  tiger  in  Soutli  America,  the  absence  of  the  civet 
cat  in  New  York,  and  that  of  the  boljohnk  or  the  Chinese  fly- 
ing fox  iu  California.  In  each  of  these  cases  there  is  no  evident 
reason  why  the  species  in  question  should  not  maintain  itself 
if  once  introduced.  The  fact  that  it  does  not  exist  is,  in  general, 
an  evidence  that  it  has  never  passed  the  barriers  which  separate 
the  region  in  question  from  its  original  home. 

Local  illustrations  of  the  same  kind  ma}^  be  found  in  moun- 
tainous regions.  In  the  Yosemite  Valley  in  California,  for  ex- 
ample, the  trout  ascend  the  Merced  River  to  the  base  of  the 
Vernal  fall.  They  cannot  rise  above  this  and  so  the  streams 
and  lakes  above  this  fall  are  destitute  of  fish. 

Examples  of  the  second  class  are  seen  in  animals  that  man 
has  introduced  from  one  country  to  another.  The  nightingale, 
the  starling,  and  the  skylark  of  Europe  have  been  repeatedly 
set  free  in  the  United  States.  But  none  of  these  colonies  has 
long  endured;  perhaps  from  lack  of  adaptation  to  the  climate, 
perhaps  from  severity  of  competition  with  other  birds,  most 
likely  because  the  few  individuals  become  so  widely  scattered 
that  they  do  not  find  one  another  at  mating  time.  In  other 
cases  the  introduced  species  has  been  better  fitted  for  the  con- 
ditions of  life  than  the  native  forms  themselves,  and  so  has 
gradually  crowded  out  the  latter.  Both  these  cases  are  il- 
lustrated aniong  the  rats.  The  black  rat  {Mns  rattus),  first 
introduced  into  America  from  Europe  about  1544,  tended  to 
crowd  out  the  native  wild  rat-s  {Sigmodon) ,  while  the  brown  rat 
(Mks  decumanus),  brought  in  still  later,  about  1775,  in  turn 
practically  exterminated  the  black  rat,  its  fitness  for  the  con- 
ditions of  life  here  being  greater  than  that  of  the  other  Eurojiean 
species. 

Of  the  third  class,  or  species  altered  in  a  new  environment, 
examples  are  numerous,  but  in  most  cases  the  causes  involved 
can  only  be  inferred  from  their  effects.  One  class  of  illusi ra- 
tions may  ])e  taken  from  island  faunas.  An  island  is  se'  off 
from  the  mainland  l^y  barriers  whicli  species  of  land  animals 
can  very  rarely  cross.  On  an  island  a  few  waifs  may  maintain 
themselves,  increasing  in  numbers  so  as  to  occupy  the  territory, 
but  in  so  doing  only  tliose  kinds  will  survive  that  can  fit  them- 
selves to  the  new  conditions.    Through  this  process  new  species 


316  EVOLUTION   AND   ANIMAL   LIFE 

will  be  formed,  like  the  parent  species  in  general  structure,  but 
having  gained  new  traits  adjusted  to  the  new  environment. 

To  processes  of  this  kind,  on  a  larger  or  smaller  scale,  the 
variety  in  the  animal  life  of  the  globe  must  be  largely  due. 
Isolation  and  adaptation  through  selection  probably  give  the 
clew  to  the  formation  of  a  very  large  proportion  of  the  "new 
species  "  in  any  group. 

It  will  be  thus  seen  that  geographical  distribution  is  primar- 
ily dependent  on  barriers  or  checks  to  the  movement  of  animals. 
The  obstacles  met  in  the  spread  of  animals  determine  the 
limits  of  the  species.  Each  species  broadens  its  range  as  far 
as  it  can.  It  attempts,  unwittingly,  of  course,  through  natural 
processes  of  increase,  to  overcome  the  obstacles  of  ocean  and 
river,  of  mountain  or  plain,  of  woodland  or  prairie  or  desert,  of 
cold  or  heat,  of  lack  of  food,  or  abundance  of  enemies — what- 
ever the  barriers  may  be.  Were  it  not  for  these  barriers,  each 
type  or  species  would  become  cosmopolitan  or  universal. 

Man  is  preeminently  a  barrier-crossing  animal;  hence,  in 
different  races  or  species,  man  is  found  in  all  regions  where 
human  life  is  possible.  The  different  races  of  men,  however, 
find  checks  and  barriers  entirely  similar  in  nature  to  those 
experienced  by  the  lower  animals,  and  the  race  peculiarities 
are  wholly  similar  to  characters  acquired  by  new  species  under 
adaptation  to  changed  conditions.  The  degree  of  hindrance 
offered  by  any  barrier  differs  with  the  nature  of  the  species 
trying  to  surmount  it.  That  which  constitutes  an  impassable 
obstacle  to  one  form  may  be  a  great  aid  to  another.  The  river 
which  blocks  the  monkey  or  the  cat  is  the  highway  of  the  fish 
or  the  turtle.  The  waterfall  which  limits  the  ascent  of  the  fish 
is  the  chosen  home  of  the  ouzel.  The  mountain  barrier  which 
the  bobolink  or  the  prairie  dog  does  not  cross  may  be  the  center 
of  distribution  of  the  little  chief  hare  or  the  Arctic  bluebird. 

The  term  fauna  is  applied  to  the  animals  of  any  region 
considered  collectively.  Thus  the  fauna  of  Illinois  comprises 
the  entire  list  of  animals  found  naturally  in  that  State.  It 
includes  the  aboriginal  man,  the  black  bear,  the  fox,  and  all  its 
animal  life  down  to  the  Amoeba  and  the  microbe  of  malaria. 
The  relation  of  the  fauna  of  one  region  to  that  of  another  de- 
pends on  the  ease  with  which  barriers  maj^  be  crossed.  Thus 
the  fauna  of  Illinois  differs  little  from  that  of  Indiana  or  Iowa, 
because  the  State  contains  no  barriers  that  animals  may  not 


GEOGRAPHICAL   DLSTRIliUTION 


317 


readily  pass.  On  the  other  liaiid,  the  fauna  of  CaUfornia  or 
Colorado  differs  materially  from  that  of  the  adjoining  regions, 
because    tlie    mountainous   country   is   full  of  barriers   which 


t 


<u 


1,     C 


o. 


V  3 
=  O 
O    w) 


J;  -r  2 

•5  5  3 

>       .  D 

C     s^  u 

Oi       £  U 

•S  =  >. 


'-  s 


'w    •;=  —    ^ 
c    =    - 


/.    r  ; 


c  > 


^        il:! 


>r   - 


obstruct  the  diffusion  of  hfe.  Distinctness  is  in  direct  i)roj)or- 
tion  to  isolation.  What  is  true  in  this  regard  of  the  fauna  of 
9,ny  region  is  hkewise  true  of  its  individual  specTes.     The  degree 


318  EVOLUTION  AND  ANIMAL  LIFE 

of  resemolance  among  individuals  is  in  strict  proportion  to  the 
freedom  of  their  movements.  Variation  within  the  hmits  of 
a  species  is  again  j^roportionate  to  the  barriers  which  prevent 
equal  and  free  diffusion. 

The  various  divisions  or  realms  into  which  the  land  surface 
of  the  earth  may  be  divided,  on  the  basis  of  the  character  of  the 
animal  life,  have  their  boundary  in  the  obstacles  offered  to  the 
spread  of  the  average  animal.  In  spite  of  great  inequalities 
in  this  regard,  we  may  yet  roughly  divide  the  land  of  the  globe 
into  seven  principal  realms  or  areas  of  distribution,  each  limited 
by  barriers,  of  which  the  chief  are  the  presence  of  the  sea  and 
the  occurrence  of  frost.  There  are  the  Arctic,  North  Tem- 
perate, South  American,  Indo- African,  Patagonian,  Lemurian, 
and  Australian  realms.  Of  these  the  Australian  realm  alone  is 
sharply  defined.  Most  of  the  others  are  surrounded  by  a  broad 
fringe  of  debatable  ground  that  forms  a  transition  to  some 
other  zone. 

The  Arctic  realm  includes  all  the  land  area  north  of  the 
isotherm  32°.  Its  southern  boundary  corresponds  closely  with 
the  northern  limit  of  trees.  The  fauna  of  this  region  is  very 
homogeneous.  It  is  not  rich  in  species,  most  of  the  common 
types  of  life  of  warmer  regions  being  excluded  by  the  cold. 
Among  the  large  animals  are  the  polar  bear,  the  walrus,  and 
certain  species  of  "ice-riding"  seals.  There  are  a  few  species 
of  fishes,  mostly  trout  and  sculpins,  and  a  few  insects;  some  of 
these,  as  the  mosquito,  are  excessively  numerous  in  individuals. 
Reptiles  are  absent  from  this  region  and  many  of  its  birds 
migTate  southward  in  the  winter,  finding  in  the  Arctic  their 
breeding  homes  only.  When  we  consider  the  distribution  of 
insects  and  other  small  animals  of  wide  diffusion  we  must  add 
to  the  AiTtic  realm  all  high  mountains  of  other  realms  whose 
summits  rise  above  the  timber  line.  The  characteristic  large 
animals  of  the  Ai^ctic,  as  the  polar  bear  or  the  musk-ox  or  the 
reindeer,  are  not  found  on  the  mountain  tops  because  barriers 
shut  them  off.  But  the  Alpine  flora,  even  under  the  equator, 
may  be  characteristically  arctic,  and  with  the  flowers  of  the 
north  may  be  found  the  northern  insects  on  whose  presence 
the  flowers  depend  for  their  fertilization  and  which  in  turn 
depend  on  these  for  their  food.  So  far  as  climate  is  concerned, 
high  altitude  is  equivalent  to  high  latitude.  On  certain 
mountains  the  different  zone^  cf  altitude  and  the  corresponding 


GEOGRAPHICAL   DISTlUBtlTION  319 

zones  of  plant  and  animal  life  are  very  sharjjly  defined.  Ex- 
cellent illustrations  are  found  in  the  San  Francisco  peaks  of 
Arizona  and  Mt.  Orizaba  in  ^lexico. 

The  North  Temperate  or  holarctic  realm  comprises  all  the 
land  between  the  northern  limit  of  trees  and  the  southern  limit 
of  forests.  It  includes,  therefore,  nearly  the  whole  of  Europe, 
most  of  Asia,  and  the  most  of  North  America.  While  there  are 
large  differences  between  the  fauna  of  North  America  and  tliat 
of  Europe  and  Asia,  these  differer.ces  are  of  minor  im])()rtance, 
and  are  scarcely  greater  in  any  case  than  the  difference  Ijetweon 
the  fauna  of  California  and  that  of  our  Atlantic  coast.  The 
close  union  of  Alaska  with  Siberia  gives  the  Arctic  region  an 
almost  continuous  land  area  from  Greenland  to  the  westward 
around  to  Norwa}^  To  the  south  everywhere  in  the  temperate 
zone  realm,  the  species  increase  in  number  and  variety,  and 
the  differences  between  the  fauna  of  North  America  and  that  of 
Europe  are  due  in  part  to  the  northward  extension  in  the  one 
and  the  otlier  of  t3^pes  originating  in  the  troi)ics. 

Especially  is  this  true  of  certain  of  the  dominant  types  of 
singing  birds.  The  group  of  wood-warblers,  tanagers,  American 
orioles,  vireos,  mocking  birds,  with  the  fly-catchers  and  hum- 
ming birds  so  characteristic  of  our  forests,  are  unrepresented  in 
Europe.  All  of  them  are  apparently  immigrants  from  the 
neotropical  realm  where  nearly  all  of  them  spend  the  winter. 
In  the  same  way  Central  Asia  has  many  immigrants  from  the 
Indian  realm  which  lies  to  the  southward.  "With  all  these 
variations  there  is  an  essential  unity  of  life  over  this  vast  area, 
and  the  recognition  of  North  America  as  a  separate  (nearctic) 
realm,  which  some  writers  have  attempted,  seems  hardly 
necessary. 

Alfred  Russell  Wallace  refers  to  this  unity  of  northern  life 
in  these  words: 

"When  an  Englishman  travels  on  the  nearest  sea  route  from  Great 
Britain  to  Northern  Japan,  he  passes  countries  very  unlike  liis  own 
both  in  aspect  and  in  natural  })roductions.  The  sunny  isles  of  the 
Mediterranean,  the  sands  and  date  palms  of  Egypt,  the  aritl  rocks  of 
Aden,  the  cocoa  groves  of  Ceylon,  the  tiger-liaunted  jungles  of  Malacca 
and  Singapore,  the  fertile  plains  and  volcanic  i)caks  of  Luzon,  the 
forest-clad  mountains  of  Formosa,  tlie  bare  hills  of  China  pass  suc- 
cessively in  review,  until  after  a  circuilous  journey  of  thirteen  thousand 


320 


EVOLUTION   AND  ANIMAL  LIFE 


miles,  he  finds  himself  at  Hakodate,  in  Japan.  He  is  now  separated 
from  his  starting  point  by  an  almost  endless  succession  of  plains  and 
mountains,  arid  deserts  or  icy  plateaus;  yet,  when  he  visits  the  interior 


Fk;. 


187. — Three  species  of  jack  rabbits  differing  in  size,  color,  and  markings,  but  be- 
lieved to  be  derived  from  one  stock.  Tne  differences  have  arisen  through  isolation 
and  adaptation.  The  upper  figure  shows  the  head  and  fore  legs  of  the  black  jack 
rabbit,  Lepics  insularis,  of  Espiritu  Santo  Island,  Gulf  of  California;  the  lower 
right-hand  figure  the  Arizona  jack  rabbit,  Lepiis  alleni,  .specimen  from  Fort  Lowell, 
Arizona;  and  the  lower  left-hand  figure  the  San  Pedro  Martir  jack  rabbit,  Lepus 
martirensis,  from  San  Pedro  Martir,  Baja  California. 


GEOGRAPHICAL   DISTRIBUTION  :^21 

of  the  country,  he  sees  so  many  familiar  natural  objects  that  he  can 
hardly  help  fancying  he  is  close  to  his  home.  lie  finils  the  woods  and 
fields  tenanted  by  tits,  hedge  sparrows,  wrens,  wagtails,  larks,  red- 
breasts, thrushes,  buntings,  and  house  sparrows;  some  aljsolutely 
identical  with  our  own  feathered  friends,  others  so  closely  resembling 
them  that  it  requires  a  practised  ornith(jlogist  to  tell  the  difference. 
.  .  .  There  are  also,  of  course,  many  birds  and  insects  which  are 
quite  new  and  peculiar,  but  these  are  by  no  means  so  numerous  or 
conspicuous  as  to  remove  the  general  impression  of  a  wonderful 
resemblance  between  the  productions  of  such  remote  islands  as  Britain 
and  Yezo."     (Island  Life.) 

A  journey  to  the  southward  from  Britain  or  Japan  or 
Illinois,  or  any  point  within  the  holarctic  realm,  would  show 
the  successive  clianges  in  the  character  of  life  though  gradual, 
to  be  still  more  rapid.  The  barrier  of  frost  which  keeps  the 
fauna  of  the  tropics  from  encroaching  on  the  northern  regions 
once  crossed,  we  come  to  the  multitude  of  animals  whose  life 
depends  on  sunshine,  the  characteristic  forms  of  the  neo- 
tropical realm. 

The  neotropical,  or  South  American  realm,  includes  South 
America,  the  West  Indies,  the  hot  coast  lands  (Tierra  Caliente) 
of  Mexico,  and  those  parts  of  Florida  and  Texas  where  frost 
does  not  occur.  Its  boundaries  through  Mexico  are  not  sharply 
defined,  and  there  is  much  overlapping  of  the  north  temperate 
realm  along  its  northern  limit.  Its  birds,  especially,  range 
widely  through  the  L'nited  States  in  the  summer  migrations,  and 
a  large  part  of  them  find  in  the  North  their  breeding  home. 
Southward,  the  broad  barrier  of  the  two  oceans  keeps  the 
South  American  fauna  very  distinct  from  that  of  Australia  or 
Africa.  The  neotropical  fauna  is  the  richest  of  all  in  species. 
The  great  forests  of  the  Amazon  are  the  treasure  houses  of  the 
naturalists.  Characteristic  tA^pes  among  the  larger  animals 
are  the  broad-nosed  (platyrrhine)  monkeys,  which  in  mUny 
ways  are  distinct  from  the  monkeys  and  apes  of  the  Old  World. 
In  many  of  them  the  tip  of  the  tail  is  highly  specialized  and  is 
used  as  a  hand.  The  Edentates  (armatlillos,  ant-eaters,  etc.) 
are  characteristically  South  American,  and  there  are  many 
peculiar  types  of  birds,  reptiles,  fishes,  and  insects. 

The  Indo-African  or  paleotropical  realm  corres})onds  to 
the  neotropical  realm  in  position.     It  includes  the  great  part 


322  EVOLUTION   AND  ANIMAL  LIFE 

of  Africa,  merging  gradually  northward  into  the  north  temper- 
ate realm  through  the  transition  districts  which  border  the 
Mediterranean.  It  includes  also  Arabia,  India,  and  the  neigh- 
boring islands,  all  that  part  of  Asia  south  of  the  limit  of  frost. 
In  monkeys,  carnivora,  ungulates,  and  reptiles  this  region  is 
wonderfully  rich.  In  variety  of  birds,  fishes,  and  insects  the 
neotropical  realm  exceeds  it.  The  monkeys  of  this  district 
are  all  of  the  narrow-nosed  (catarrhine)  type,  various  forms 
being  much  more  nearly  related  to  man  than  is  the  case  with 
the  pecuUar  monkeys  of  South  America.  Some  of  these 
(anthropoid  apes)  have  much  in  common  with  man.  To  this 
region  belong  the  elephant,  the  rhinoceros,  and  the  hippopot- 
amus, as  well  as  the  tiger,  lion,  leopard,  giraffe,  the  wild  asses, 
and  horses  of  various  species,  besides  a  large  number  of  rumi- 
nant animals  not  found  in  other  parts  of  the  world.  It  is,  in 
fact,  in  the  lower  mammals  and  reptiles  that  its  most  striking 
distinctive  characters  are  found.  In  its  fish  fauna  it  has  much 
in  common  with  South  America. 

The  Lemurian  realm  comprises  Madagascar  alone.  It  is 
an  isolated  division  of  the  Indo- African  realm,  but  the  presence 
of  man}^  species  of  lemurs — an  unspecialized  or  primitive  type 
of  monkey — is  held  to  justify  its  recognition  as  a  distinct  realm. 
In  most  other  groups  of  animals  the  fauna  of  Madagascar  is 
essentially  that  of  neighboring  parts  of  Africa. 

The  Patagonian  realm  includes  the  south  temperate  zone 
of  South  America.  It  has  much  in  common  with  the  neo- 
tropical realm  from  which  its  fauna  is  mainly  derived,  but  the 
presence  of  frost  is  a  barrier  which  vast  numbers  of  species  can- 
not cross.  Beyond  the  Patagonian  realm  lies  the  Antarctic 
continent.  The  scanty  fauna  of  this  region  is  little  known, 
and  it  probably  differs  from  the  Patagonian  fauna  chiefly  in 
the  absence  of  all  but  the  ice-riding  species. 

The  Australian  realm  comprises  Australia  and  neighboring 
islands.  It  is  more  isolated  than  any  of  the  others,  having 
been  protected  by  the  sea  from  the  invasions  of  the  character- 
istic animals  of  the  Indo-African  and  temperate  realms.  It 
shows  a  singular  persistence  of  low  or  pri<mitive  types  of  ver- 
tebrate life,  as  though  in  the  process  of  evolution  the  region 
had  been  left  a  whole  geologie  age  behind.  If  the  competing 
faunas  of  Africa  and  India  could  have  been  able  to  invade 
Australia,  the  dominant  mammals  and  birds  of  that  region 


GEOGRAPHICAL  DISTRIBUTION  323 

•  Would  not  have  been  left  as  they  are  now — marsupials  and 
parrots. 

It  is  only  when  barriers  have  shut  out  competition  tliat 
simple  or  unspecialized  types  abound.  The  Larger  the  land 
area  and  the  more  varied  its  surface,  the  greater  is  the  stress 
of  competition  and  the  more  specialized  are  the  characteristic 
forms.  As  part  of  this  specialization  is  in  the  direction  of 
hardiness  and  power  to  persist,  the  species  from  the  large  areas, 
as  a  whole,  are  least  easy  of  extermination.  The  rapid  multi- 
plication of  rabbits  and  foxes  in  Australia,  when  introduced 
by  the  hand  of  man,  shows  what  might  have  taken  ])lace  in  this 
country  had  not  impassable  barriers  of  ocean  shut  them  out. 

Each  of  these  great  realms  may  be  indefinitely  sul)divid(>d 
into  provinces  and  sections,  for  there  is  no  end  to  the  possi- 
bility of  analysis.  No  farm  has  exactly  the  same  animals  or 
])lants  as  any  other,  as  finally  in  ultimate  analysis  we  find  tliat 
no  two  animals  or  plants  are  exactly  alike.  Shut  off  one  ])air 
of  animals  from  the  otliers  of  its  species,  and  its  descendants 
will  differ  from  the  parent  stock.  The  difference  increases 
with  time  and  with  distance  so  long  as  the  separation  is  main- 
tained. Hence  new  species  and  new  fauna  or  aggregations  of 
species  are  produced  wherever  free  diffusion  is  checked  by  any 
kind  of  barrier. 

In  like  manner,  w^e  may  divide  the  ocean  into  faunal  areas 
or  zones,  according  to  the  distribution  of  its  animals.  For 
this  purpose  the  fishes  probabh^  furnish  the  best  indications, 
although  results  very  similar  are  obtained  wlien  we  consider 
the  mollusks  or  the  Crustacea. 

The  pelagic  fishes  are  those  which  inhabit  the  o})en  sea, 
swimming  near  the  surface,  and  often  in  great  schools.  Sucli 
forms  are  usually  confined  to  the  warmer  waters.  They  are  for 
tha  most  part  predatory  fishes,  strong  swinuners,  and  many 
of  the  species  are  found  in  all  warm  seas.  Most  species  have 
spec'al  homing  waters,  to  whicli  they  repair  in  the  spawning 
season.  To  the  free-swimming  forms  of  invertel)rates  and 
■protozoa,  found  in  the  open  ocean,  the  name  Plankton  is  ap- 
plied. 

The  bassalian  fauna,  or  deep-sea  fauna,  is  comj^osed  of 
species  inhabiting  great  depths  (from  2,500  to  25,000  feet)  in 
the  sea.  At  a  short  distance  below  the  siu'face  the  cliange  in 
temperature  from  day  to  night  is  no  longer  felt.     At  a  still 


324  EVOLUTION  AND  ANIMAL  LIFE 

lower  depth  there  is  no  difference  between  winter  and  summer, 
and  still  lower  none  between  day  and  night.  The  bassalian 
fishes  inhabit  a  region  of  great  cold  and  inky  darkness.  Their 
bodies  are  subjected  to  great  pressure,  and  the  conditions  of 
life  are  practically  unvarying.  There  is,  therefore,  among  them 
no  migration,  no  seasonal  change,  no  spawning  season  fixed 
by  outside  conditions,  and  no  need  of  adaptation  to  varying 
environment.  As  a  result,  all  are  uniform  indigo-black  or 
purple  in  color,  and  all  show  more  or  less  degeneration  in  those 
characters  associated  with  ordinary  environment.  Their  bodies 
are  elongate,  from  the  lack  of  specialization  in  the  vertebrae. 
The  flesh,  being  held  in  place  by  the  great  pressure  of  the 
water,  is  soft  and  fragile.  The  organs  of  touch  are  often  highly 
developed.  The  eye  is  either  excessively  large,  as  if  to  catch 
the  slightest  ra}^  of  light,  or' else  it  is  undeveloped,  as  if  the 
fish  had  abandoned  the  effort  to  see.  In  many  cases  luminous 
spots  or  lanterns  are  developed  by  which  the  fish  may  see  to 
guide  its  way,  and  in  some  forms  these  shining  appendages 
are  highly  developed.  In  one  form  (lEthoprora)  a  luminous 
body  covers  the  end  of  the  nose,  like  the  headlight  of  an  engine. 
Many  of  these  species  have  excessively  large  teeth,  and  some 
have  been  known  to  swallow  animals  actually  larger  than 
themselves.  Those  w^hich  have  lanternlike  spots  have  always 
large  eyes. 

The  deep-sea  fishes,  however  fantastic,  have  all  near  rela- 
tives among  the  shore  forms.  Most  of  them  are  degenerate 
representatives  of  w^ell-known  types — ^for  example,  of  eels,  cod, 
smelt,  grenadiers,  sculpin,  and  flounders.  The  deep-sea  crus- 
taceans and  moilusks  are  similarly  related  to  shore  forms. 

The  third  great  subdivision  of  marine  animals  is  the  littoral 
or- shore  group,  those  living  in  w^ater  of  moderate  depth,  never 
venturing  far  into  the  open  sea  either  at  the  surface  or  in  the 
depths.  This  group  shades  into  both  the  preceding.  The 
individuals  of  some  of  the  species  are  excessively  local,  remain- 
ing their  life  long  in  tide  pools  or  coral  reefs  or  piles  of  rock. 
Others  venture  far  from  home,  becoming  more  or  less  pelagic. 
Still  others  ascend  rivers  either  to  spawn  (anadromous,  as  the 
salmon,  shad,  and  striped  bass),  or  for  purposes  of  feeding,  as 
the  robalo,  corvina,  and  other  shore  fishes  of  the  tropics. 
Some  live  among  rocks  alone,  some  in  seaweed,  some  on  sandy 
shores,  some  in  the  surf,  and  some  only  in  sheltered  lagoons. 


GEOGRArHICAL  DISTRIBUTION  325 

In  all  seas  there  are  fishes  and  otlicr  marine  animals,  and  each 
creatm'e  haunts  the  i)hices  for  whicli  it  is  fitted. 

There  is  the  closest  possible  aniilo«]i;y  between  the  variations 
of  species  of  animals  or  jjlants  in  (HITerent  districts  and  that  of 
words  in  different  languages.  Tlie  language  of  any  people  is 
not  a  unit.  It  is  made  up  of  words  which  have  at  various 
times  and  under  various  conchtions  come  into  it  fr(jm  the  speech 
of  other  people.  The  granunar  of  a  language  is  an  expression 
of  the  mutual  relations  of  these  words.  The  word  as  it  exists 
in  any  one  language  represents  the  species.  Its  cognate  or  its 
ancestor  in  any  other  language  is  a  related  species.  The  words 
used  in  a  given  district  at  any  one  time  constitute  its  ])liil()- 
logical  fauna.  There  is  a  struggle  for  existence  between  woids 
as  among  animals.  For  example  the  words  hcgiji  and  commence, 
shake  and  agitate,  work  and  operate  (Saxon  and  French)  are  in 
the  English  language  constantly  b.ought  into  competition. 
The  fittest,  the  one  that  suits  English  ])urposes  best,  will  at 
last  survive.  If  both  have  elenunits  of  fitness,  tl:e  field  will 
be  divided  between  them.  The  silent  letters  in  words  tell  their 
past  history,  as  rudimentary  organs  tell  what  an  animal's 
ancestry  has  been.  This  analogy,  of  course,  is  not  perfect  in 
all  regards,  as  the  passing  of  the  words  from  mouth  to  mouth 
is  not  rigidly  comparable  with  the  generation  of  animals. 

We  may  illustrate  the  formation  of  species  of  animals  by 
following  any  widely  used  word  across  Europe.  Tluis  the 
Greek  aster  becomes  in  Latin  and  Italian  stella;  whence  the 
Spanish  estrella  and  the  French  etoile.  In  Germany  it  becomes 
Stern,  in  Danish  Stjern;  whence  the  Scottish  starn  and  English 
star. 

In  like  manner,  the  name  cherry  may  be  traced  from  country 
to  country  to  which  it  has  been  taken  in  cultivation.  Its  Greek 
name,  kerasos,  becomes  cei^asus,  ceresia,  ceriso,  cereso,  cerise, 
among  the  Latin  nations.  This  word  is  shortened  to  Kirsrh 
and  Kers  with  the  people  of  the  North.  In  England,  chcrys, 
cherry,  are  obviously  derived  from  cerise. 

The  study  of  a  fauna  or  a  flora  as  a  whole  is  thus  analogous 
to  tlie  study  of  a  living  language.  The  evolution  of  a  language 
corresponds  to  the  history  of  the  life  of  some  region.  Fhilology, 
systematic  zo()logy,  and  botany  are  alike  intimately  related  to 
geograpliy.  Tlie  parallelism  betw(H'ii  speech  districts  and 
faunal  districts  has  been  manv  times  notcth  The  spread  of  a 
22 


326  EVOLUTION  AND  ANIMAL  LIFE 

language,  like  the  spread  of  a  fauna,  is  limited  by  natural 
barriers.  It  is  the  work  of  civilization  to  break  down  these 
barriers  as  limiting  the  distribution  of  civilized  man.  The 
dominant  languages  cross  these  barriers  with  the  races  of  man 
who  use  them,  and  with  them  go  the  domesticated  animals 
and  plants  and  the  weeds  and  vermin  man  has  brought  un- 
willingly into  relations  of  domination. 

The  profitable  study  of  the  problems  of  geographical  dis- 
tribution is  possible  only  on  the  theory  of  the  derivation  of 
species.  If  we  view  all  animals  and  plants  as  the  results  of  spe- 
cial creations  in  the  regions  assigned  to  them,  we  have  instead 
of  laws  only  a  jumble  of  arbitrary  and  meaningless  facts.  In 
our  experience  with  the  facts  of  science  w^e  have  learned  that 
no  fact  is  arbitrary  or  meaningless.  We  know  no  facts  which 
lie  beyond  the  realm  of  law.  We  nnay  close  with  the  language 
of  Asa  Gray: 

"When  we  gather  into  one  line  the  several  threads  of  evidence  of 
this  sort  we  find  that  they  lead  in  the  same  direction  with  the  views 
furnished  by  other  lines  of  investigation.  Slender  indeed  each  thread 
may  be,  but  they  are  manifold,  and  together  they  bind  us  firmly  to 
the  doctrine  of  the  derivation  of  species.'' 


,**-^ 


chait]':r  xm 

ADAPTATIONS 

It  is  a  wise  provision  of  nature  that  trees  shall  not  grow  up  into 
the  skv. — Goethe. 

The  adaptation  of  every  species  of  animal  and  j)lant  to  its 
environment  is  a  matter  of  every  da}'  observation.  80  perfect 
is  this  adaptation  in  its  details  that  its  main  facts  tend  to 
escape  our  notice.  The  animal  is  fitted  to  the  air  it  breathes, 
the  water  it  drinks,  the  food  it  finds,  the  cUmate  it  endures, 
the  region  which  it  inhabits.  All  its  organs  are  fitted  to  its 
functions:  all  its  functions  to  its  environment.  Organs  and 
functions  are  alike  spoken  of  in  a  half-figurative  v/ay  as  con- 
cessions to  environment.  And  all  structures  and  powers  are 
in  this  sense  concessions,  in  another  sense,  adaptations.  As 
the  loaf  is  fitted  to  the  pan,  or  the  river  to  its  bed,  so  is  each 
species  fitted  to  its  surroundings.  If  it  were  not  so  fitted,  it 
would  not  live.  But  such  fitness  on  the  vital  side  leaves  large 
room  for  variety  in  characters  not  essential  to  the  life  of  the 
animal.  Thus  we  ascribe  nonessential  characters  to  vaiiation, 
preserved  by  heredity  and  guarded  by  isolation.  ^'ital  or 
adaptive  characters  originate  in  the  same  way,  ])ut  th.ese  are 
preserved  in  heredity  and  guarded  and  intensified  by  selection. 

The  strife  for  place  in  the  crowd  of  animals  makes  it ,  neces- 
sary for  each  one  to  adjust  itself  to  the  ])lace  it  holds.  As  the 
individual  becomes  fitted  to  its  condition,  so  nuist  ihc  sj^ecies 
as  a  whole.  The  species  is  therefore  maile  up  of  individuals 
that  are  fitted  or  may  become  fitt(Ml  for  the  conditions  of  life. 
As  the  stress  of  existence  becomes  more  severe,  the  individuals 
fit  to  continue  the  species  are  chosen  more  closely.  This  choice 
is  the  autom.atic  work  of  the  conditions  of  life,  but  it  is  none 
the  less  effective  in  its  operations,  and  in  the  course  of  centuries 

327 


328 


EVOLUTION   AND   ANIMAL   LIFE 


it  ma}^  be  considered  unerring.  When  conditions  change,  the 
perfection  of  adaptation  in  a  species  may  be  the  cause  of  its 
extinction.  If  the  need  of  a  special  fitness  cannot  be  met, 
immediately  the  species  will  disappear.  For  example,  the 
native  sheep  of  England  have  developed  a  long  wool  fitted  to 
protect  them  in  a  cool,  damp  climate.  Such  sheep,  transferred 
to  Cuba,  died  in  a  short  time,  leaving  no  descendants.  The 
warm  fleece,  so  useful  in  England,  rendered  them  wholly  unfit 


Fig.  188. — Nest  of  T'espa,  a  social  wasp.     (Photograph  by  A.  L.  ilelander  and 

C.  T.  Brues.) 


for  survival  in  the  tropics.  It  is  one  advantage  of  man,  as 
compared  with  other  forms  of  life,  that  so  many  of  his  adapta- 
tions are  external  to  his  structure,  and  can  be  cast  aside  when 
necessity  arises. 

The  great  fact  of  nature  is  adaptation.  But  while  general 
adaptation  to  widespread  conditions  is  universal,  there  exist 
also  a  multitude  and  variety  of  special  adaptations  fitting 
organisms  to  special  conditions.  These  special  adaptations 
arrest  our  attention  to  a  greater  degree  than  general  adaptations 
because  they  furnish  the  element  of  contrast. 

The  various  types  of  special  adaptations  may  be  roughly 
divided  into  five  classes  as  follows:  (a)  Food-securing;  (b)  self- 


ADAFFATIOXS 


329 


defense;  (c)  defense  of  young;  (<:/)  rivalry;  (e)  adjustment  to 
surroundings. 

For  the  purpose  of  capture  of  tlioir  prey,  most  carnivorous 
animals  are  provided  with  strong  claws,  sharp  teeth,  hooked 
beaks,  and  other  structures  familiar  to  us  in  the  hon,  tiger, 
dog,  cat,  owl,  and  eagle.  Insect- eating  mammals  have  con- 
trivances especially  a(la})ted  for  the  catching  of  insects.  The 
ant-eater,  for  exam})le,  has  a  long  sticky  tongue  which  it  tlirust.s 
forth  from  its  cvlindrical 
snout  deep  into  the  recesses 
of  the  ant-hill,  bringing  it 
out  with  its  surface  covered 
with  ants.  Animals  which 
feed  on  nuts  are  fitted  with 
strong  teeth  or  beaks  for 
cracking  them.  Strong  teeth 
are  found  in  those  fishes 
which  feed  on  crabs,  or  sea 
urchins.  Those  mammals 
like  the  horse  and  cow,  that 
feed  on  plants,  have  usually 
broad  chisellike  incisor  teeth 
for  cutting  off  the  foliage, 
and  teeth  of  very  similar 
form  are  developed  in  dif- 
ferent groups  of  plant-eating 
fishes.  Molar  teeth  are  found 
when  it  is  necessary  that  the 
food    should    be   crushed   or 

chewed,  and  the  sharp  canine  teeth  go  with  a  flesh  diet.  The 
long  neck  of  the  giraffe  enables  it  to  browse  on  the  foliage  of 
trees  in  grassless  regions. 

Insects  like  the  leaf-beetles  and  the  grasshoppers,  that  feed 
on  the  foliage  of  plants,  have  a  pair  of  jaws,  broad  but  sharply 
edged,  for  cutting  off  bits  of  leaves  and  stems.  Those  which 
take  only  liquid  food,  as  the  butterflies  and  sucking  bugs, 
have  their  mouth  parts  modified  to  form  a  slender,  hollow 
sucking  beak  or  ])roboscis,  which  can  be  thrust  into  a  flcnvcr 
nectary,  or  into  the  green  tissue  of  ]^lants  or  the  flesh  of  animals 
to  suck  up  nectar  or  ])lant  sap,  or  blood,  according  to  the 
.s])ecial  food  habits  of  the  insect.     The  honey-bee  has  a  very 


FiTi.  Ib'J. —  i  nc  iirijwti  i)cln:iii,  .-In  a\  iiiu  i;iii:ir 
sac  which  it  uses  in  catching  antl  holilinK 
fishes  for  its  food. 


EVOLUTION  AND  ANIMaL  LIFE 


complicated  equipment  of  mouth  parts  fitted  for  taking  either 
sohd  food  hke  pollen^  or  Hquid  food  Jike  the  nectar  of  flowers. 
The  mosquito  has  a  "bilP^  composed  of  six  sharp,  slender 
needles  for  piercing  and  lacerating  the  flesh,  and  a  I:ng 
tubular  under  lip  through  which  the  blood  can  flow  into  the 
mouth.  Some  predaceous  insects,  as  the  praying  horse  (Fig. 
38),  have  their  fore  legs  developed  into  formidable  grasping 
organs  for  seizing  and  holding  their  prey. 


Fig.  190. — Ant-lion  larva  plowing  its  way  through  the  sand  (ur-:jer  figure),  while  an- 
other is  commencing  the  excavation  of  a  funnel-shaped  pit  similar  to  one  on  right. 
(Photograph  by  A.  L.  Melander  and  C.  T.  Brues.) 


For  self-protection  the  higher  animals  depend  largely  on 
the  same  organs  and  instincts  as  for  the  securing  of  food.  Car- 
nivorous beasts  use  tooth  and  claw  in  their  own  defense  as 
well  as  in  securing  their  prey,  but  these  as  well  as  other  animals 
may  protect  themselves  in  other  fashions.  Many  of  the  higher 
animals  are  provided  with  horns,  structures  useless  in  procuring 
food,  but  effective  as  weapons  of  defense.  Others  defend 
themselves  by  blows  with  their  strong  hoofs.  Among  the 
reptiles  and  fishes  and  even  among  the  mammals,  the  defensive 
coat  of  mail  is  found  in  great  variety.  The  turtle,  the  armadillo, 
the  sturgeon,  and  gar  pike,  all  these  show  the  value  of  defensive 
armature,  and  bony  shield'?  are  developed  to  a  still  greater 


ADAm'ATTOXS 


331 


degree  in  various  extinct  types  cf  fishes.  Tlie  cnil)  anil  lobster 
with  claws  and  carapace  are  well  defended  against  their  enemies, 
and  the  hermit  crab,  with  its  trick  of  thrust in^  its  unprotected 
body  within  a  cast-off  sheU  of  a  sea  snail,  finds  in  this  instinct 
a  perfect  defense.  Insects  also,  especially  beetles,  are  protected 
by  their  coats  of  mail.  Scales  and  spines  of  many  sorts  serve 
to  defend  the  l)odies  of  rep- 
tiles and  fishes,  while  feathers 
protect  the  bodies  of  birds 
and  hair  those  of  most 
mammals. 

The  ways  in  wliich  ani- 
mals make  themselves  dis- 
agreeable or  dangerous  to 
their  captors  are  almost  as 
varied  as  the  animals  them- 
selves. Besides  the  teeth, 
claws,  and  horns  of  ordinar}^ 
attack  and  defense,  we  find 
among  the  mammals  many 
special  structures  or  con- 
trivances which  serve  for 
defense  through  making  their 
possessors  unpleasant.  The 
scent  glands  of  the  skunk 
and  its  relatives  serve  as 
examples.  The  porcupine  has 
the  bristles  in  its  fur  special- 
ized as  quills,  barbed  and 
detachable.  These  quills  fill 
the   mouth   of   an   attacking 

wolf  or  fox,  and  serve  well  the  purpose  of  defense.  The 
hedgehog  of  Europe,  an  animal  of  different  nature,  being  re- 
lated rather  to  the  mole  than  to  the  squirrel,  has  a  similar 
armature  of  quills.  The  armadillo  of  the  tropics  has  movable 
shields,  and  when  it  withdraws  its  head  (also  defended  by  a 
bony^  shield)  it  is  as  well  ])rotected  as  a  turtle. 

The  turtles  are  all  i)rotected  by  bony  shields,  and  some  of 
them,  the  box  turtles,  n^iiy  close  tluMr  shields  almost  hermet- 
ically. The  snakes  broaden  their  heads,  swell  their  necks,  or 
show  their  forked  tongues  to  frighten  their  enemies.     Some  of 


Fig.  191. — Scorpion  showing  the  siicoial 
development  of  certain  numth  i)arts  (the 
maxillary  palpi)  as  pincorlike  organs  for 
grasping.  On  the  posterior  tip  of  the 
body  is  the  poison  sting. 


332 


EVOLUTION   AND   ANIMAL   LIFE 


them  are  further  armed  with  fangs  connected  with  a  venom 
gland,  so  that  to  most  animals  their  bite  is  deadly.     Besides 


Fig.  192. — Cocoon  enclosing  a  pupa  of  the  great  Ceanothus  moth,  Samia  ceanothi, 

spun  by  the  larva  before  pupation. 


its  fangs  the  rattlesnake  has  a  rattle  on  the  tail  made  up  of  a 
succession  of  bony   clappers,   modified  vertebrae,   and   scales, 

by  which  intruders  are  warned  of  its  pre- 
sence. This  sharp  and  insistent  buzz  is  a 
warning  to  animals  of  other  species  and 
perhaps  a  recognition  signal  to  those  of  its 
kind. 

Even  the  fishes  have  many  modes  of 
self-defense  through  giving  pain  or  injury 
to  animals  who  would  swallow  them.  The 
catfish  or  horned  pout  when  attacked  sets 
immovably  the  sharp  spine  of  the  pectoral 
fin,  inflicting  a  jagged  wound.  Pelicans 
which  have  swallowed  a  catfish  have  been 
known  to  die  of  the  wounds  inflicted  by 
the  fish's  spine.  In  the  group  of  scorpion 
fishes  and  toad  fishes  are  certain  genera 
in  which  these  spines  are  provided  with 
poison  glands.  These  may  inflict  very 
severe  wounds  to  other  fishes,  or  even  to 
birds  or  man.  One  of  this  group  of  poison 
fishes  is  the  nohi  (Emmydrichthys).  A 
group  of  small  fresh-water  catfishes,  known 
as  the  mad  toms,  have  also  a  poison  gland 
attached  to  the  pectoral  spine,  and  the 
sting  is  most  exasperating,  like  the  sting 


Fig.  193. — Larva  of  swal- 
lowtail butterfly,  Pa- 
pilio  cresphontes , 
showing  osmateria 
(eversible  processes 
giving  off  an  ill  odor) 
projected.  (After 
photograph  by  Slinger- 
.land.) 


ADAinWTIOXS 


333 


of  the  wasp.  The  sting-rays  (Fig.  194),  of  which  there  are 
many  species,  have  a  strong  jagged  spine  on  the  tail,  covered 
with  shme,  and  armed  with  broatl  sawUke  teeth.  Tliis  in- 
flicts a  dangerous  wound,  not  through  the  presence  of  spe- 
cific venom,  but  from  the  (hmger  of  Ijlood  poisoning  aris- 
ing from  the  shme,  and  the  ragged  or   unch'an    cut. 

The  i)oisonous  alkaloids 
within  the  flesh  of  some  fishes 
{Tetraodon,  Balistes,  etc.) 
serve  to  destroy  the  enemies 
of  the  species  while  sacrific- 
ing the  individual.  Thes.^ 
alkaloids,  most  develo;)e:l  in 
the  spawning  season,  p:-o- 
duce  a  disease,  known  in 
man  as  ciguatera.  This  is 
rarely  known  outside  of  the 


tropics. 

Many  fishes  are  defended 
bv  a  coat  of  mail  or  a  coat 
of  sharp  thorns.  Tlie  globe 
fishes  and  porcupine  fishes 
are  for  the  most  part  de- 
fended by  spines,  but  their 
instinct  to  swallow  air' gives 
them  an  additional  safeguard. 
When  one  of  these  fishes  is 
disturbed  it  rises  to  the  sur- 
face, gulps  air  until  its  capa- 
cious stomach  is  filled,  and 
then  floats  belly  upward  on 

the  water.  It  is  thus  protected  from  other  fishes,  though  easily 
taken  by  man.  The  torpedo,  electric  eel,  electric  catfish,  and 
star-gazer,  sur])rise  and  stagger  their  ca})tors  by  means  of  electric 
shocks.  In  the  torpedo  or  electric  ray  (Fig.  195),  of  whicli 
species  are  found  on  the  sandy  shores  of  all  warm  seas,  on 
either  side  of  the  head  is  a  large  honeycomblike  structure 
which  yields  a  strong  electric  shock  whenever  the  live  fish  is 
touclied.  This  shock  is  felt  severely  if  the  fish  be  stabbed  witli 
a  knife  or  metallic  spear.  The  electric  ei'l  of  the  rivers  of 
Paraguay  and  southern  Brazil  is  said  to  give  severe  shocks  to 


Fig.  194. — StiiiK-ray,  Vrolophua  goodei, 
fruui  Pauama. 


334 


EVOLUTION   AND   ANIMAL   LIFE 


herds  of  wild  horses  driven  through  the  streams,  and  similar 
accounts  are  given  of  the  electric  catfish  of  the  Nile.  In 
tropical  seas,  the  tangs  or  surgeon  fishes  (Hepatus)  are  provided 
with  a  knifelike  spine  on  the  side  of  the  tail,  the  sharp  edge 
directed  forward  and  slipping  into  a  sheath.  This  is  a  formi- 
dable weapon  when  the  fish  is 
alive. 

Other  fishes  defend  them- 
selves by  spears  (sword  fish, 
spear  fish,  sailfish)  or  by  saws 
(sawfish,  sawshark)  or  by  pad- 
dles, (paddlefish).  Others  still, 
make  use  of  sucking  disks  of 
one  sort  or  another  (as  in  the 
snailfish,  the  clingfish,  and  the 
goby),  to  cling  to  the  under 
side  of  rocks,  or  as  in  the 
Remora  to  the  bodies  of  swift- 
moving  sharks.  Blind  fishes  in 
the  caves  are  adapted  to  their 
condition,  the  eyes  being  obso- 
lete, wliile  the  skin  is  covered 
with  rows  of  sensitive  papillae. 
In  similar  circumstances  sala- 
manders, crayfishes,  and  insects 
are  also  blind.  There  are  also 
blind  gobies  which  live  in  the 
crevices  of  rocks  and  still  other 
blind  fishes  in  the  great  depths 
of  the  sea. 
Some  fishes,  like  the  lancelet,  lie  buried  in  the  sand  all  their 
lives.  Others,  as  the  sand  darter  (Ammocrypta  pellucida)  and 
the  hinalea  (Julis  gaimardi),  bury  themselves  in  the  sand  at 
intervals  to  escape  from  their  enemies.  Some  five  in  the 
cavities  of  tunicates  or  sponges  or  holothurians  or  corals  or 
oysters,  often  passing  their  whole  lives  inside  the  cavity  of  one 
animal.  Many  others  hide  themselves  in  the  interstices  of 
kelp  or  seaweeds.  Some  eels  coil  themselves  in  the  crevices 
of  rocks  or  coral  masses,  striking  at  their  prey  lik^  snakes. 
Some  sea-horses  cling  by  their  tails  to  gulfweed  or  ser. -wrack. 
Many  little  fishes  {Gobiomorus,  Carangus,  Psenes)  cluster  under 


Fig.  195. — Torpedo  or  electric  ray, 
Narcine  brasiliensis,  showing  elec- 
tric cells. 


ADAPTATIONS  .^^^o 

the  stinging  tentacles  of  tlie  roituguese  man-of-war  or  under 
ordinary  jelly  fishes. 

Some  fishes  called  tiie  flying  fishes  sail  througii  the  air  with 
a  grasshopperhke  motion  tliat  closely  iinitates  true  fliglit. 
The  long  pectoral  fins,  winglike  in  form,  cuimot,  however,  be 
flapped  by  the  fish,  the  muscles  serving  only  to  expand  or  fold 
them.  These  flshes  live  in  the  open  sea  or  ojumi  channels, 
swimming  in  large  schools.     The  small   species   fly   for  a   few 

■anni .  ..  r~ ■ — • -— — . ^, 


-r 


4^^-- 


V-    s 


Fig.  196. — Flying  fi.slies:  'I'lie  upijcr  one.  a  species  of  Ci/pselnrKs;  the  lower,  of 
Exocoetus.  These  fishes  escape  from  their  enemies  by  leai)inK  into  the  air 
and  sailing  or  "flying"  i<jng  ilistances. 

feet  only,  the  large  ones  for  more  than  an  eighth  of  a  mile. 
These  mav  rise  five  to  twentv  feet  above  the  water. 

The  flight  of  one  of  the  largest  flying  fishes  {Ci/pselurus  cali- 
fornicus)  has  been  carefully  studied  by  Dr.  Cliarles  H.  Gilbert 
and  the  senior  author.  The  movements  of  the  fish  in  the  water 
are  extremely  ra})id.  The  sole  motive  power  is  the  action 
under  the  water  of  the  strong  tail.  No  force  can  be  acquired 
while  the  fish  is  in  the  air.  On  rising  from  the  water  the  move- 
ments of  the  tail  are  continuous  until  the  whole  body  is  out  of 
the  water.  When  the  tail  is  in  motion  the  ])ect()rals  seem  in 
a  state  of  rai)id  vibration.  This  is  not  ])roduced  by  muscular 
action  on  the  fins  themselves.  It  is  the  body  of  the  fish  which 
vil^rates,  the  pectorals  })rojecting  farthest  having  the  greatest 
ami)litude  of  movement.      \Vliile  the  tail  is  in  the  water  tlie 


336  EVOLUTION   AND   ANIMAL   LIFE. 

ventral  fins  are  folded.  When  the  action  of  the  tail  ceases 
the  pectorals  and  ventrals  are  spread  out  wide  and" held  at  rest. 
They  are  not  used  as  true  wings,  but  are  held  out  firmly,  acting 
as  parachutes,  enabling  the  body  to  skim  through  the  air. 
When  the  fish  begins  to  fall  the  tail  touches  the  water.  As 
soon  as  it  is  in  the  water  it  begins  its  motion,  and  the  body 
with  the  pectorals  again  begins  to  vibrate.  The  fish  may,  by 
skimming  the  water,  regain  motion  once  or  twice,  but  it  finally 
falls  into  the  water  with  a  splash.  While  in  the  air  it  suggests 
a  large  dragon  fly.  The  motion  is  very  swift,  at  first  in  a 
straight  line,  but  is  later  deflected  in  a  curve,  the  direction 
bearing  little  or  no  relation  to  that  of  the  wind.  When  a 
vessel  passes  through  a  school  of  these  fishes,  they  spring  up 
before  it,  moAdng  in  all  directions,  as  grasshoppers  in  a  meadow. 

Among  the  insects,  the  possession  of  stings  is  not  uncom- 
mon. The  wasps  and  bees  are.  familiar  examples  of  stinging 
insects,  but  many  other  kinds,  less  familiar,  are  similarly  pro- 
tected. All  insects  have  their  bodies  covered  with  a  coat  of 
armor,  composed  of  a  horny  substance  called  chitin.  In  some 
cases,  this  chitinous  coat  is  very  thick  and  serves  to  protect 
them  effectually.  This  is  especially  true  of  the  beetles.  Some 
insects  are  inedible,  and  are  conspicuously  colored  so  as  to 
be  readily  recognized  by  insectivorous  birds.  The  birds, 
knowing  by  experience  that  these  insects  are  ill-tasting,  avoid 
them.  Others  are  effectively  concealed  from  their  enemies 
by  their  close  resemblance  in  color  and  marking  to  their 
surroundings.  These  protective  resemblances  are  discussed 
in  Chapter  XIX. 

To  the  category  of  structures  which  may  be  useful  in  self- 
defense  belong  the  many  peculiarities  of  coloration  known  as 
"recognition  marks.''  These  are  marks,  not  otherwise  helpful, 
which  are  supposed  to  enable  members  of  any  one  species  to 
recognize  its  kind  among  the  mass  of  animal  life.  To  this 
category  belongs  the  black  tip  of  the  weasel's  tail,  which  re- 
mains the  same  whatever  the  changes  in  the  outer  fur.  Another 
example  is  seen  in  the  white  outer  feathers  of  the  tail  of  the 
meadow  lark  as  well  as  in  certain  sparrows  and  warblers. 
The  white  on  the  skunk's  back  and  tail  may  serve  the  same 
purpose  and  also  as  a  warning.  It  is  apparently  to  the  skunk's 
advantage  not  to  be  hidden,  for  to  be  seen  in  the  crowd  of  ani- 
mals is  to  be  avoided  by  them.    That  recognition  is  the  actual 


ADAl^ATIONS 


337 


function  of  such  markings  has  never  been  clearly  proved.  The 
songs  of  birds  and  the  calls  of  various  creatures  may  serve  also 
as  recognition  marks.  Each  species  knows  and  heeds  its  own 
characteristic  song  or  cry,  and  it  is  a  source  of  nnitual  ])ro- 
tection.  The  fur-seal  pup  knows  its  motlier's  call,  even  liioiigh 
ten  tliousand  other  mothers  are  calling  on  I  lie  same  rookery. 

In  questions  of  attack  and  defense,  tlie  need  of  fighting 
animals  of  their  own  kind,  as  well  as  animals  of  other  races, 
must  be  considered.  To  struggles 
of  species  with  those  of  their  own 
kind,  tlie  term  rivalr}'  may  be  ap- 
plied. Actual  warfare  is  confined 
mainly  to  males  in  the  breeding 
ser.son,  especially  in  ])olygamous 
species.  Among  those  in  which 
the  male  mates  with  many  females, 
he  must  struggle  with  otlier  males 
for  their  possession.  In  all  the 
groups  of  vertebrates  the  sexes 
are  about  equal  in  numbers. 
Among  monogamous  animals,  which 
mate  for  the  season  or  for  life, 
there  is  less  occasion  for  destruc- 
tive rivalry. 

Among  monogamous  birds,  or 
those  which  pair,  the  male  courts 
the  female  of  his  choice  by  song 
and  by  display  of  his  bright 
feathers.  According  to  the  theory 
of  sexual  selection,  the  female  con- 
sents to  be  chosen  by  the  one  which  jileases  her.  It  is  as- 
sumed that  the  handsomest,  most  vivacious,  and  most  nuisi- 
cal  males  are  the  ones  most  successful  in  such  courtship. 
With  polygamous  animals  there  is  intense  rivalry  among  th.e 
males  in  the  mating  season,  which  in  almost  all  sjKH'ies  is  in 
the  spring.  The  strongest  males  survive  and  reproduce  their 
strength.  Tlie  most  notable  athiptation  is  seen  in  the  superior 
size  of  teeth,  horns,  mane,  or  spurs.  Among  the  polygamous 
fur  seals  and  sea  lions  the  male  is  abo\it  four  times  tlie  size  of 
the  female.  In  the  i)olyganious  family  of  deer.  bulTal(\.  anil 
the  domestic  cattle  aud  shcep^  the  male  is  larger  and  more 


Fig.  197. — Egg  case  of  the  Cali- 
fornia barndoor  skate,  liaja 
hinoculata.  cut  open  to  show 
young  inside.  Young  issues 
naturally  at  cue  end  of  the 
skate. 


338  EVOLUTION   AND   ANIMAL   LIFE 

powerfully  armed  than  the  female.  In  the  polygamous  group 
to  which  the  hen,  turkey,  and  peacock  belong,  the  males  pos- 
sess the  display  of  plumage,  and  the  structures  adapted  for 
fighting,  with  the  wdll  to  use  them. 

The  protection  of  the  young  is  the  source  of  many  adaptive 
structures  as  well  as  of  the  instincts  by  which  such  structures 
are  utilized.  In  general  those  animals  are  highest  in  develop- 
ment, with  the  best  means  of  holding  their  own  in  the  struggle 
for  life,  that  take  best  care  of  their  young.  Those  instincts 
which  lead  to  home  building  are  all  adaptations  for  preserving 


Fig.  198. — The  snake,  Ichthyophis  glutinosus,  with  egg  case  carried  in  coils  of  the  body, 

(After  Goebel  and  Selenka.) 

the  young.  Among  the  lower  or  more  coarsely  organized  birds, 
such  as  the  chicken,  the  duck,  and  the  auk,  as  with  the  reptiles, 
the  young  animal  is  hatched  with  Avell-developed  muscular 
system  and  sense  organs,  and  is  capable  of  running  about,  and, 
to  some  extent,  of  feeding  itself.  Birds  of  this  type  are  known 
as  prsecocial,  while  the  name  altricial  is  applied  to  the  more 
highly  organized  forms,  such  as  the  thrushes,  doves,  and  song 
birds  generally.  With  these  the  young  are  hatched  in  a  wholly 
helpless  condition,  with  ineffective  muscles,  deficient  senses, 
and  dependent  wholly  upon  the  parent.  The  altricial  condition 
demands  the  building  of  a  nest,  the  establishment  of  a  home, 
and  the  continued  care  of  one  or  both  of  the  parents. 

The  very  lowest  mammals  known,  the  duck  bills  (Mono- 
tremes)  of  Australia,  lay  large  eggs  in  a  strong  shell  like  those 
of  a  turtle,  and  these  they  guard  with  great  jealousy.     But 


ADAPTATIONS 


339 


with  almost  all  mammals  the  o<rg  is  very  small  and  without 
much  food  yolk.     The  egg  begins  its  development  within  tiic 


r~ 


>v/' 


1 


in..  I'J'J. —  Jvai.^;. .;.',,,  Macropus  rufus,  with  young  in  pouch. 


body.  It  is  nourished  by  the  blood  of  the  mother,  and  after 
birth  the  voims;  is  cherished  bv  her.  and  fed  bv  milk  secreted 
by   speciaUzed   glands   of   the   skin.     All   these   features   are 


340 


EVOLUTION  AND  ANIMAL  LIFE 


Fig.  .200. — Egg  case  of  the 
cockroach. 


adaptations  tending  toward  the  preservation  of  the  young. 
In  the  Marsupials,  which  stand  next  to  the  Monotremes — the 
Ivangaroo,  opossum,  etc. — the  young  are  born  in  a  very  im- 
mature state  and  are  at  once  seized  by  tlie  mother  and  thrust 
into  a  pouch  or  fold  of  skin  along  the  abdomen,  where  they  are 

kept  until  they  are  able  to  take  care 
of  themselves  (Fig.  199).  This  is  a 
singular  adaptation,  but  less  special- 
ized and  less  perfect  than  the  condi- 
tion found  in  ordinary  mammals. 

Among  the  insects,  the  special  .pro- 
visions for  the  protection  and  care  of 
the  eggs  and  the  young  are  widespread  and  various.  The  eggs 
of  the  common  cockroach  are  laid  in  small  packets  inclosed 
in  a  firm  wall  (Fig.  200) .  The  eggs  of  the  great  water  bugs 
are  carried  on  the  back  of  the  male  (Fig.  201):  and  the  spiders 
lay  their  eggs  in  a  silken  sac  or  cocoon,  and  some  of  the  ground 
or  running  spiders  (Lycosidce) ,  drag  this  egg  sac,  attached  to 
the  tip  of  the  abdomen,  about  with 
them.  The  young  spiders  when  hatched 
live  for  some  days  inside  this  sac,  feed- 
ing on  each  other.  Many  insects  have 
long,  sharp,  piercing  ovipositors,  by 
means  of  which  the  eggs  are  thrust  into 
the  ground  or  into  the  leaves  or  stems 
of  green  plants,  or  even  into  the  hard 
wood  of  tree  trunks.  Some  of  the  scale 
insects  secrete  wax  from  their  bodies 
and  form  a  large,  often  beautiful  egg 
case  attached  to  and  nearly  covering 
the  body  in  which  eggs  are  deposited. 
The  various  gall  insects  lay  their  eggs 
in    the    soft    tissue   of  plants,    and   on 

the  hatching  of  the  larva  an  abnormal  growth  of  the  plant 
occurs  about  the  young  insect,  forming  an  inclosing  gall  that 
serves^  not  only  to  protect  the  insect  within,  but  to  furnish 
it  with  an  abundance  of  plant  sap,  its  food.  The  young  in- 
sect remains  in  the  gall  until  it  completes  its  development 
and  growth,  when  it  gnaws  its  way  out.  Such  insect  galls  are 
especially  abundant  on  oak  trees  (Figs.  202  and  203). 

The  movements  of  migratory  fishes  are  mainly  controlled 


Fig.  201. — Giant  waterbug, 
Serphus,  male  carrying 
eggs  on  its  back. 


ADAPTATIONS 


341 


by  the  impulse  of  reproduction.  Some  pelagic  fislies,  especially 
those  of  the  mackerel  and  flying  fish  families,  swim  long  dis- 
tances to  a  region  favorable  for  the  deposition  of  spawn.  Others 
pursue  for  equal  distances  the  schools  of  herring,  menhaden,  or 
other  fishes  which  serve  as  their  prey.  Some  species  are  known 
mainl}^  in  tlie  waters  they  make  their  breeding  homes,  as  in 


^ 


■   > 


f    ■♦; 


,-'^    :«     N   \ 


Fig.  202. — Galla  on  the  rose  caused  by  the  gall  fly,  Rhoditea  rosce.     (After  Kieffer.) 


Cuba,  southern  California,  Hawaii,  or  Japan,  the  individuals 
being  scattered  at  other  times  through  the  wide  seas. 

Many  fresh- water  fishes^  as  trout  and  suckers,  forsake  the 
large  streams  in  the  spring,  ascending  the  small  brooks  where 
their  young  can  be  reared  in  greater  safety.  Still  others, 
known  as  anadromous  fishes,  feed  and  mature  in  the  sea,  but 
ascend  the  rivers  as  the  im]nilse  of  reproduction  grows  strong. 
Among  such  fishes  are  the  salmon,  shad,  alewife,  sturgeon,  and 
striped  bass  in  American  waters.  The  most  remarkable  case 
23 


342 


EVOLUTION   AND   ANIMAL   LIFE 


of  the  anadromous  instinct  is  found  in  the  king  salmon  or 
qumnat  {Oncorhyiichus  tschaivytscha)  of  the  Pacific  Coast. 
This  great  fish  spawns  in  November,  at  the  age  of  four  years 
and  with  an  average  weight  of  twenty-two  pounds.  In  the 
Columbia  River  it  begins  running  with  the  spring  freshets  in 
March  and  April.  It  spends  the  whole  summer  without  feeding 
in  the  ascent  of  the  river.     By  the  autumn,  the  individuals 


Fig.  203. — Giant  gall  of  the  white  oak  (California)  made  by  the  gall  fly,  Andricvs  cali- 
fornicus;  the  gall  at  the  right  cut  open  to  show  the  tunnels  made  by  the  insects  in 
escaping  from  the  gall.     (From  photograph.) 


have  reached  the  mountain  streams  of  Idaho,  greatly  changed 
in  appearance,  discolored,  worn,  and  distorted.  The  male  is 
humpbacked,  with  sunken  scales  and  greatly  enlarged,  hooked, 
bent,  or  twisted  jaws,  w^ith  enlarged  doglike  teeth.  On  reach- 
ing the  spawning  beds,  which  may  be  a  thousand  miles  from 
the  sea  in  the  Columbia,  over  two  thousand  miles  in  the  Yukon, 
the  female  deposits  her  eggs  in  the  gravel  of  some  shallow  brook. 
The  male  covers  them  and  scrapes  the  gravel  over  them. 
Then  both  male  and  female  drift  tail  foremost  helplessly  down 
the  stream:  none,  so  far  as  certainly  known,  ever  survives  the 
reproductive  act.  The  same  habits  are  found  in  the  four  other 
species  of  salmon  in  the  Pacific,  but  in  most  cases  the  individuals 
do  not  start  so  early  nor  run  so  far.  The  blueback  salmon  or 
redfish,  however,  does  not  fall  far  short  in  these  regards.  The 
salmon  of  the  Atlantic  has  a  similar  habit,  but  the  distance 
traveled  is  everywhere  mucli  less,  and  the  hook-jawed  males 


ADAPTATIONS 


343 


drop  back  clown  to  the  sea  and  survive  to  repeat  the  acts  of 
reproduction. 

Catadronious  fishes,  as  the  true  eel  (An(iuill(i),  reverse  this 
order,  fce(Hng  in  the  rivers  and  l)rackish  estuaries,  apparently 
finding  their  usual  spawning  ground  in  tlie  sea. 

A  large  part  of  the  life  of  the  animal  is  a  struggle  with  the 
environment  itself:  in  this  str\iggle  only  tliose  that  are  adapted, 
live  and  leave  descendants  fitted  like  themselves,  'i'lie  fur  of 
mammals  fits  them  to  their  surroundings.  As  the  fur  differs 
so  may  the  habits  change.  Some  animals  are  active  in  winter: 
others,  as  the  bear,  and  in  Northern  Japan,  the  red-faced  mon- 
key, hibernate,  sleeping  in  caves  or  hollow  trees  or  in  burrows, 
until  conditions  are  favorable  for  their  activity."*  Most  snakes 
and  lizards  hibernate  in  cold  weather.  In  the  swami)S  of 
Louisiana,  in  winter,  the  bottom  may  often  be  seen  covered 
with  water  snakes  lying  as  inert  as  ilead  twigs.  Usually, 
however,  hibernation  is  accompanied  by  concealment.     Some 


u 


Fig... 204. — Head  of  rainbow  trmit,  ^(i.'mo  irnU-us,  witu  yiii  cover  beut  back  u>  show 

gills,  the  breathing  organs. 


animals  in  hibernation  may  be  frozen  alive  without  aj^parent 
injury.  The  blackfish  of  the  Alaska  swam]-)s,  fed  to  tlogs  when 
frozen  solid,  has  been  known  to  revive  in  the  heat  of  tlie  dog's 
stomach  and  to  wriggle  out  and  escai)e.  As  animais  resist 
heat  and  cold  by  adaptations  of  structure  and  habits,  so  may 
they  resist  dryness.  Certain  fishes  hold  reservoirs  of  water 
above  their  gills,  by  means  of  which  they  can  breathe  during 


344 


EVOLUTION   AND   ANIMAL   LIFE 


•A 


Fig.  205. — Tree  toad,  Hyla  regilla. 


short   excursions   from  the  water.     Still  others    (mud  fishes) 

retain  the  primitive  lunghke  structure  of  the  swim  bladder, 

and  are  able  to  breathe  air  when,  in  the  dry  season,  the  water 

of  the  pools  is  reduced 
to  mud. 
~  Another     series     of 

adaptations  is  con- 
cerned with  the  places 
-  chosen  by  animals  for 
their  homes.  The  fishes 
that  live  in  the  water 
have  special  organs  for 
breathing  under  water 
(Fig.   204).      Many   of 

the  South  American  monkeys  have  the  tip  of  the  tail  adapted 

for  cHnging  to  hmbs  of  trees  or  to  the  bodies  of  other  monkeys 

of.  its  own  kind.     The  hooked  claws  of   the  bat  hold  on  to 

rocks,  the  bricks  of   chimneys,  or  to  the 

surface   of   hollow   trees,    where    the    bat 

sleeps  through  the  day.      The  tree  frogs 

or  tree  toads  (Fig.  205)  have  the  tips  of 

the  toes   swollen,  forming   Httle  pads  by 

which  they  cling  to  the  bark  of  trees. 

Among    other  adaptations  relating    to 

special  surroundings  or  conditions   of  hfe 

are  the  great  cheek  pouches  of  the  pocket 

gophers,  which  carry  food,  as  grass-roots 

and  the  like,  when  the  gopher  excavates  its 

burrow. 

Those  insects  which  live  underground, 

making   burrows    or    tunnels    in   the   soil, 

have  their  legs  or  other  parts  adapted  for 

digging  and  burrowing.     The  mole  cricket 

(Figs.  206  and  207)  has  its  legs  stout  and 

short,  with  broad,  shovellike  feet.     Some 

water  beetles   and   water  bugs   have   one 

or  more  of  the  pairs  of  legs  flattened  and 

broad  to  serve  as  oars  or  paddles  for  swim- 
ming.    The  grasshoppers  or  locusts,   which   leap,  have  their 

hind  legs  greatly  enlarged  and  elongated,  and  provided  with 

strong  muscles  so  as  to  make  of  them  "leaping  legs.'"     The 


Fig.  206. —  The  mole 
cricket,  Gryllotalpa, 
with  fore  legs  modi- 
fied for  digging. 


ADAPTATION'S 


345 


grubs  or  larvae  of  boctlos  which  hve  as  "borers"  in  tree  trunks 
have  mere  riulinients  of  legs,  or  none  at  all.  They  have  great, 
strong,  l)iting  jaws  for  cutting  away  the  hard  wood.  They 
move  simply  by  wriggling  jilong  in  their  burrows  or  tunnels. 

Insects  that  live  in  wr.ter  either  come 
up  to  the  surface  to  breathe  or  take  down 
air  underneath  their  wings,  or  in  some  other 
way,  or  have  gills  for  breathing  the  air 
which  is  mixed  with  the  water.  Tliese  gills 
are  special  adaptive  structures  which  present 
a  great  variety  of  form  and  a])i)earance.  In 
the  young  of  the  May  flies  they  are  delicate 
platelike  flaps  projecting  from  the  sides  of 
the  body.  Tliey  are  ke])t  in  constant 
motion,  gently  waving  back  and  forth  in 
the  water  so  as  to  maintain  currents  to 
bring  fresh  water  in  contact  with  them. 
Young  mosquitoes  do  not  have  gills,  but 
come  up  to  the  surface  to  breathe.  The 
larvae,  or  wrigglers,  breathe  through  a  special 
tube  at  the  posterior  tip  of  the  body,  while 
the  pupse  have  a  pair  of  hornlike  tubes  on 
the  back  of  the  head  end  of  the  body. 

Many  fishes,  chiefly  of  the  deep  seas, 
develop  organs  for  producing  light.  These 
are  known  as  luminous  organs,  phosphor- 
escent organs,  or  photophores.  These  are 
independently  developed  in  four  entirely 
unrelated  groups  of  fishes.  This  difference 
in  origin  is  accompanied  by  corres])onding 
differences  in  structure.  The  best  known 
type  is  found  in  the  Iniomi,  including  the 

lantern    fishes    and    their    many    relatives.  

They  may  have  luminous  spots,  differentiated  areas,  round  or 
oblong,  which  shine  starlike  in  the  dark.  Tliese  are  usually 
symmetrically  placed  on  the  sides  of  the  Ixxly.  They  may 
have  also  luminous  glands  or  diffuse  areas  which  are  luminous, 
but  which  do  not  show  tlie  specialized  structure  of  the  ]>hos- 
phorescent  spots.  These  glands  of  similar  nature  to  the  spots 
are  mostly  on  the  herd  or  tail.  In  oiie  gen\is.  .^thoprnrn,  the 
luminous  snout  is  compared   to  the  headlight   of  an  engine. 


Fig.   207. — Front    leg 
_of  the  mole  cricket, 
showing  nt  e  open- 
ing of  uuilitory  or- 
gan.    (.\fter  Sharp.) 


346 


EVOLUTION   AND  ANIMAL  LIFE 


d.  -<i' 


^-.^1=^. -^  -_-rr- 


Entire!}^  different  ?.re  the  p^:otop':orcs  in  the  midshipman  or 
singing  fish  (Porichthys) ,  a  genus  of  the  toad  fishes  or  Batra- 
choididse.  These  species  Uve  near  the  shore  and  the  lumi- 
nous spots  are  outgrowths  from  pores  of  tlie  lateral  line. 

In  one  of  the  anglers   (Cory nolo phiis  reinhardti)  the  com- 
plex bait,  is  said  to  be  luminous,  and  luminous  areas  occur 

on  the  belly  of  a  very 
small  shark  of  the  deep 
seas  of  Japan  {Etmopterus 
lucifer) .  Dr.  Peter  Schmidt 
of  St.  Petersburg  has  a 
drawing  of  this  shark 
made  at  night  from  its 
own  light. 

While  among  the 
higher  or  vertebrate  ani- 
mals, especially  the  fishes 
and  reptiles,  most  remark- 
able cases  of  adaptations 
occur,  3^et  the  structural 
changes  are  for  the  most 
part  external,  usually  not 
affecting  fundamentally 
the  development  of  the  internal  organs  other  than  the  skeleton. 
The  organization  of  these  higher  animals  is  much  less  plastic 
than  that  of  the  invertebrates.  In  general,  the  higher  the 
type  the  more  persistent  and  unchangeable  are  those  struc- 
tures not  immediately  exposed  to  the  influence  of  the  struggle 
for  existence.  It  is  thus  the  outside  of  an  animal  that  tells 
where  its  ancestors  have  lived.  The  inside,  suffering  little 
change  whatever  the  surroundings,  tells  the  real  nature  of  the 
animaL 


■,■■',.:.'-    ■•::   ■ 


Fig.  208. — Nest  of  the  trapdoor  spider. 


/: 


4   /> 


1»r•9>^»-*^-<•' 


CHAPTER   X\n 
PARASITISM   AND   DEGENERATION 

Les  causes  dc  IV'volutioii  re<!;rossiv"  j^'uvcnt  so  niniciicr  :\  uiio 
seule,  la  limitation  des  moyeiis  de  suhsistaiico,  dc  Im,  la  lutto  jtour 
Texistence  entre  les  or<!;anisnies  ou  Ics  sociotrs.  ct  entre  leurs  parties 
composantes. — Demooh,  Massakt,  and  Vandekvelde. 

A  SPECIAL  kind  of  adaptation  is  that  shown  by  parasitic 
animals.  The  relations  of  parasitic  animals  to  their  hosts 
appear  in  many  familiar  exam])les,  and  the  results  of  this  para- 
sitic life,  or  at  least  the  conditions  that  seem  always  to  attend 
it,  namely  the  degeneration,  slight  or  extreme,  of  the  ])arasites, 
is  also  familiar  to  all  observers  of  animal  life.  The  term  para- 
sitism, as  well  as  the  term  degeneration,  cannot  be  very 
rigidly  defined.  To  prey  upon  the  bodies  of  other  animals  is 
the  common  habit  of  many  creatures.  If  the  animals  which 
live  in  this  way  are  free,  chasing  or  lying  in  wait  for  or  snaring 
their  prey,  we  speak  of  them  in  general  as  predatory  animals. 
But  if  they  attach  themselves  to  the  body  of  their  jn-cy  or 
burrow  into  it,  and  are  carried  about  by  it,  live  on  or  in  it, 
then  we  cjdl  them  ])arasites.  Ai;d  the  difTerencc  in  habit 
between  a  lion  and  an  intestinal  worm  is  large  enough  and 
marked  enough  to  make  very  clear  to  us  what  is  meant  wIkmi  wo 
speak  of  one  as  predatory  and  the  other  as  a  ])arasite.  Hut 
how  shall  we  class  the  lam})rey,  that  swims  about  imtil  it  finds 
a  fish  to  which  it  clings,  while  sucking  away  its  blood?  It 
lives  mostly  free,  hunting  its  j^rey,  clinging  to  it  for  a  while, 
and  is  carried  about  by  it.  Closely  related  to  the  lampreys 
are  the  hag  fishes  (}fi/xine)  marine  eellike  fishes  that  attach 
themselves  by  a  suckerlike  mouth  to  living  fishes  and  gradually 
scrape  and  eat  their  way  into  the  abdominal  c'avity  of  the  liost. 
These  "hags"  or  "borers"  aj)proach  more  nearly  to  the  cou- 

.T17 


348 


EVOLUTION   AND   ANIMAL   LIFE 


dition  of  an  internal  parasite  than  any  other  vertebrate.  And 
what  about  the  flea?  In  its  immature  Ufe  it  hves  as  a  white 
grub  or  larva  in  the  dust  of  cracks  and  crevices,  of  floors  and 
cellars  and  heaps  of  debiis;  here  it  pupates,  and  finally  changes 
into  the  active  leaping  blood-sucking  adult  which  finds  its  way 
to  the  body  of  some  mammal  and  clings  there  sucking  blood. 
But  it  can  jump  off  and  hunt  other  prey;  it  leaves  the  host  body 
entirely  to  lay  its  eggs,  and  yet  it  feeds  as  a  parasite,  at  least 
it  conforms  to  the  definition  of  parasite  in  the  essential  fact  of 


Fig.  209. — At  the  left,  the  red-tailed  trichina  fly,  Winthemia,  U-pastulata,  the  parasite 
of  the  army  worm,  Leucania  unipuncta ;  at  the  right,  the  worms  upon  which  the 
fly  has  laid  eggs.     (After  Slingerland.) 


being  carried  about  on  or  in  the  host  bod}^  while  feeding  at  the 
host's  expense. 

It  is  of  course  not  particularly  important  that  we  distinguish 
sharply  between  parasitic  and  predaceous  animals,  but  as  we 
look  on  the  degeneration  of  parasitic  animals  as  the  result  of 
their  special  habit  of  life,  we  must  attempt  a  sort  of  classifica- 
tion of  the  phases  or  degrees  of  parasitism,  in  order  to  asso- 
ciate with  them  corresponding  categories  of  degeneration. 

The  bird  Hce  (Mallophaga),  which  infest  the  bodies  of  all 
kinds  of  birds  and  are  found  especially  abundant  on  domestic 
fowls,  live  upon  the  outside  of  the  bodies  of  their  hosts,  feeding 
upon  the  feathers  and  dermal  scales.  They  are  examples  of  ex- 
ternal parasites.  Other  examples  are  fleas  and  ticks,  and  the 
crustaceans  called  fish  lice  and  whale  lice,  which  are  attached 
to  marine  animals.  On  the  other  hand,  almost  all  animals 
are  infested  by  certain  parasitic  worms  which  live  in  the  ali- 
mentary canal,  like  the  tapeworm,  or  imbedded  in  the  muscles, 
like  the  trichina.  These  are  examples  of  internal  parasites. 
Such  parasites  belong  mostly  to  the  class  of  worms,  and  some 


PARASITISM   AND   DEGENERATION  349 

of  them  arc  very  injurious,  siickirif!^  the  ])Uj()(1  from  the  tissues 
of  the  host,  while  others  feed  soU^ly  on  the  ])artly  digested 
food.  There  are  also  ])arasites  tliat  live  partly  within  and 
partly  on  the  outside  of  the  body,  like  the  ^acculina,  whieh 
lives  on  various  kinds  of  crabs.  The  body  of  the  Saccidina 
consists  of  a  soft  sac  which  lies  on  the  outside  of  the  crab's 
body,  and  of  a  niunber  of  lon^;,  slender  root  like  ])rocesses 
which  penetrate  deei)ly  into  the  crab's  body,  and  take  up 
nourishment  from  within.  The  Sacculina  is  itself  a  crus- 
tacean or  crablike  creature.  The  classification  of  })arasites 
as  external  and  internal  is  purely  arbitrary,  but  it  is  often  a 
matter  of  convenience. 

Some  parasites  live  for  their  whole  lifetime  on  or  in  the 
body  of  the  host,  as  is  the  case  with  the  bird  lice.  Their  eggs 
are  laid  on  the  feathers  of  the  bird  host;  the  young  when  hatched 
remain  on  the  bird  during  growth  and  development,  and  the 
adults  only  rarely  leave  the  body,  usually  never.  These  may 
be  called  permanent  parasites.  On  the  other  hand,  fh^as  lea}) 
off  or  on  a  dog  apparently  as  caprice  dictates;  or,  as  in  other 
cases,  the  parasite  may  pass  some  definite  part  of  its  life  as  a 
free  nonparasitic  organism,  attaching  itself,  after  develoi)ment, 
to  some  animal,  and  remaining  there  for  the  rest  of  its  life. 
These  parasites  may  be  called  temporary  parasites.  But  this 
grouping  or  classification,  like  that  of  the  external  and  internal 
parasites,  is  simply  a  matter  of  convenience,  and  does  not 
indicate  at  all  any  blood  relationship  among  the  members  of 
any  one  group. 

Some  parasites  are  so  specialized  in  habit  and  structure  that 
they  are  wholly  unable  to  go  through  their  life  history,  or  to 
maintain  themselves,  except  in  a  single  fixed  way.  They  are 
dependent  wholly  on  one  particular  kind  of  host,  or  on  a  par- 
ticular series  of  hosts,  part  of  their  life  being  ]:)assed  in  one  and 
another  part  in  one  or  more  other  so-calUnl  intermediate  hosts. 
These  parasitic  species  are  called  obligate  parasites,  while 
others  with  less  definite,  more  flexible  retiuirements  in  regard 
to  their  mode  of  development  and  life  are  called  facultative 
parasites.  These  latter  may  indeed  be  able  to  go  through  life 
as  free-living,  nonparasitic  animals,  although,  with  oi>por- 
tunity,  they  live  parasitically. 

In  nearly  all  cases  the  boily  of  a  j)arasite  is  simpler  in 
structure  than  the  body  of  otlicr  animals  which  are  closely 


350  EVOLUTION  AND  ANIMAL  LIFE 

related  to  the  parasite — that  is,  animals  that  live  parasitically 
have  simpler  bodies  than  animals  that  live  free  active  lives, 
competing  for  food  with  the  other  animals  about  them.  This 
simplicity  is  not  primitive,  but  results  from  the  loss  or  atrophy 
of  the  struct'ores  which  the  mode  of  life  renders  useless.  Many 
.parasites  are  attached  firmly  to  their  host,  and  do  not  move 
about.  They  have  no  need  of  the  power  of  locomotion.  They 
are  carried  by  their  host.  Such  parasites  are  usually  without 
wings,  legs,  or  other  locomotory  organs.  Because  they  have 
given  up  locomotion  they  have  no  need  of  organs  of  orientation, 
those  special  sense  organs  like  eyes  and  ears  and  feelers  which 
serve  to  guide  and  direct  the  moving  animal;  and  most  non- 
locomotory  parasites  will  be  found  to  have  no  eyes,  nor  any 
of  the  organs  of  special  sense  which  are  accessory  to  locomotion 
and  which  serve  for  the  detection  of  food  or  of  enemies.  Be- 
cause these  important  organs,  which  depend  for  their  success- 
ful activity  on  a  highly  organized  nervous  sj^stem,  are  lacking, 
the  nervous  system  of  parasites  is  usually  ver}^  simple  and  un- 
developed. Again,  because  the  parasite  usually  has  for  its 
sustenance  the  already  digested  highly  nutritious  food  elabo- 
rated by  its  host,  most  parasites  have  a  very  simple  alimentary 
canal,  or  even  no  alimentary  canal  at  all.  Finally,  as  the  fixed 
parasite  leads  a  wholly  sedentary  and  inactive  life,  the  break- 
ing down  and  rebuilding  of  tissue  in  its  body  go  on  very  slowly 
and  in  minimum  degree,  and  there  is  no  need  of  highly  developed 
respiratory  and  circulatory  organs,  so  that  most  fixed  parasites 
have  these  systems  of  organs  in  simple  condition.  Altogether 
the  body  of  a  fixed,  permanent  parasite  is  so  simplified  and  so 
wanting  in  all  those  special  structures  which  characterize  the 
higher,  active,  complex  animals,  that  it  often  presents  a  very 
different  appearance  from  those  animals  with  which  w^e  know 
it  to  be  nearly  related. 

The  simplicity  of  parasites  does  not  indicate  that  they 
belong  to  the  groups  of  primitive  simple  animals.  Parasitism 
is  found  in  the  whole  range  of  animal  fife,  from  primitive  to 
highest,  although  the  vertebrate  animals  include  very  few  para- 
sites and  these  of  little  specialization  of  habit.  But  their 
simplicity  is  something  that  has  resulted  from  their  mode  of 
life.  It  is  the  result  of  a  change  in  the  body  structure  which 
we  can  often  trace  in  the  development  of  the  individual  para- 
site.    Many  parasites  in  their  young  stages  are  free,  active 


PARASITISM  AND   DEGENERATION 


351 


animals  with  a  ])ctter  or  more  complex  body  than  they  possess 
in  their  fully  developed  or  adult  sta^e.  The  simplicity  of 
parasites  is  the  result  of  defeneration — a  degeneration  that 
has  been  brought  about  by  their  adoption  of  a  sedentary,  non- 
competitive parasitic  life.  And  tliis  simi)hcity  of  degenera- 
tion, and  the  simplicity  of  primitiveness  should  be  sharj)ly 
distinguished.  Animals  that  are  primitively  simple  have  had 
only  simple  ancestors;  animids  that  are  simj)lc  by  degeneration 
often  have  had  highly  organized,  complex  ancestors.  And 
while  in  the  life  history  or  develojHnent  of  a  primitively  simple 
animal  all  the  young  stages  are  sim])ler  than  the  adult,  in  a 
degenerate  animal  the  young  stages  may 
be,  and  usually  are,  more  complex  and 
more  highly  organized  than  the  adult 
stage. 

In  the  few  examples  of  parasitism 
(selected  from  various  animal  groups) 
that  are  described  in  the  following  pages 
all  these  general  statements  are  illus- 
trated. 

In  the  intestines  of  crayfishes,  centi- 
pedes, and  several  kinds  of  insects  may 
often  be  foimd  certain  one-celled  animals 
(Protozoa)  which  are  living  as  parasites. 
Their  food,  which  they  take  into  their 
minute  body  by  absorption,  is  the  intes- 
tinal fluid  in  which  they  lie.  These  parasitic  Protozoa  belong 
to  the  genus  Gregarina.  Because  the  body  of  any  protozoan 
is  as  simple  as  an  animal's  body  can  well  be,  being  com- 
posed of  ])ut  a  single  cell,  degeneration  cannot  occur  in  the 
cases  of  these  parasites.  There  are,  besides  Gregarina,  many 
other  parasitic  one-celled  animals,  several  kinds  living  inside 
the  cells  of  their  host's  body.  Several  kinds  of  these  liave 
been  proved  to  be  the  causal  agents  of  serious  human  diseases. 
Conspicuous  among  these  are  the  minute  ))arasitic  S})orozoa 
which  are  the  actual  cause  of  the  malarial  and  similar  fevers 
that  rack  the  human  bodv  in  nearlv  all  imrts  of  the  world. 
•  In  the  class  of  Sporozoa  (of  the  great  ])ranch  Protozoa  or 
one-celled  animals)  is  an  order  callcil  Ileniosporidia  (or  llemo- 
cytozoa)  C()m]:)rising  numerous  kinds  of  unicellular  parasites 
which  live  in  the  blood  of  vertebrates  (with  certain  inverte- 


FiG.  210.  —  The  w-ingless 
bat-tick,  Xi/cferihia, 
(After  Slicirp;  much  en- 
larged.) 


352 


EVOLUTIO^^  AND  ANIMAL  LIFE 


brates  us  intermediate  or  alternate  liosts).  Certain  kinds  are 
found  in  the  cold  blood  of  fishes,  amphibians,  reptiles,  and 
certain  others  in  the  warm  blood  of  birds  and  mammals.  The 
genera  Halteridium  and  Plasmodium  contain  certain  species 
that  live  exclusively  in  the  blood  of  birds  or  mammals  for  part 
of  their  life  and  in  the  bodies  of  certain  arthropods  for  the 
other  part  of  their  life.  They  produce  a  series  of  asexual 
generations  (reproduction  by  simple  division  or  sporulation) 
in  their  vertebrate  hosts,  and  a  sexual  generation  (reproduction 

by  the  development 
of  a  zygote  formed 
by  the  fusion  of  two 
cells,  called  gametes) 
in  the  arthropod  host. 
This  arthropod  host 
for  all  the  species  so 
far  known  of  these 
genera  is  exclusively 
the  mosquito.  Three 
species  of  the  genus 
Plasmodium,  namely, 
P.  vivax,  P.  malarim, 
and  P.  falciparu7n,  are 
the  specific  causal 
agents  of  the  distinct 
malarial  fevers  known 
as  tertian,  quartan, 
and  tropical  fever  re- 
spectively. (In  the 
literature  of  "mosquitoes  and  malaria, '^  the  name  " Hmna- 
moeba"  will  be  found  to  be  used  synonymously  with  Plas- 
modium.) 

Laveran,  a  French  surgeon  in  Algiers,  discovered  the  Plas- 
modium parasite  in  the  red  blood  corpuscles  of  malarial  fever 
patients  in  1880,  and  determined  that  the  disease  was  actually 
and  solely  due  to  the  destructive  and  toxic  effects  of  the  growth 
and  multiplication  of  the  parasite  in  the  blood.  Every  forty- 
eight  hours  in  tertian  fever  (seventy-two  hours  in  quartan)  there 
is  completed  a  whole  (asexual)  cycle  in  the  life  of  one  of  these 
parasites,  including  its  birth  by  the  division  of  the  body  of 
the  mother  into  several  small  merozoites,  the  penetration  of 


Fig.  211. — The  life  cycle  of  Coccidiurn  lithobii.  Proto- 
zoan parasite  of  the  centipede,  Lithobius.  (After 
Schaudinn.) 


PARASITISM   AND   DEGENERATION  353 

a  red  blood  corpuscle  by  each  of  tliese  merozoites,  the  growth 
of  the  parasite  in  tlie  blood  corj)uscle  at  the  expense  of  the 
corpuscle,  the  maturing  and  sporulation  (or  division  into  new 
merozoites)  of  the  parasite,  and  tlie  final  breakdown  of  tlie 
corpuscle  and  release  into  the  l)lood  ])lasma  of  the  tiny  active 
merozoite.  Numerous  generations  of  this  type  are  ])roduced 
in  tlie  blood  of  a  patient,  but  finally  a  sort  of  senescence  or 
degeneration  of  the  parasite  sets  in,  and  unless  there  is  a  fresh 
infection  of  the  patient  from  outside,  the  parasitic  host  dimin- 
ishes and  finally  nearly  disai)pears.  If  the  effects  of  the  para- 
site have  not  been  too  severe  during  the  height  of  its  invasion 
the  imtient  now  recovers. 

For  the  continued  multiplication  and  persistence  of  the 
parasitic  species  a  new  })rocess  or  set  of  conditions  is  necessary. 
If  a  drop  of  blood  drawn  from  a  malarial  ])atient  is  examined 
under  the  microscope  the  parasitic  individuals  abundantly  in 
evidence  in  this  blood  will  be  seen  to  manifest  a  curious  be- 
havior within  a  few  minutes.  Some  of  them  will  move  and 
sc[uirm  about  with  great  activity,  and  extend  and  retract 
pseudopodiumlike  processes,  until  finally  with  great  rai)idity 
a  few  (usually  four  to  six)  delicate  threadlike  fiagella  or 
flagellalike  i)rocesses  will  shoot  out  from  the  body  mass  and 
break  away  from  it.  These  motile  fiagella  are  really  gametes 
or  sexual  cells  of  one  type  (the  male)  while  other  large  nearly 
immobile  sub-spherical  parasite  individuals  which  do  not  be- 
have as  these  do  are  gametes  or  sexual  cells  of  the  otiier  (or 
female)  type.  The  fiagella  find  and  penetrate  or  fuse  with  the 
larger  gametes  and  form  a  zygote  or  resting  egg  cell. 

While  the  processes  just  described  have  been  taking  place 
in  the  blood  droplet  under  our  microscope,  as  a  matter  of  fact 
this  normally  takes  place  in  the  stomach  of  a  mosquito.  For 
when  a  mosc^uito  (at  least  of  a  certain  kind)  sucks  blood  from 
a  malarial  patient  the  blood  parasites  are  of  course  taken  in 
also  and  deposited  in  the  stomach  where  digestion  of  the  l)l()od 
begins.  Now  when  the  zygotes  are  formed  in  the  mosquito's 
stomach  they  do  not  remain  lying  in  the  stomach  cavity  but 
move  to  the  wall  of  the  stomach  and  i)artially  penetrate  it. 
As  many  as  five  hundr(Hl  zygotes  have  been  found  in  the 
stomach  walls  of  a  single  mosfpiito.  The  zygote  now  in- 
creases rapidly  in  size,  becoming  a  j)erceptible  nodule  on  the 
outer  side  of  the  stomach  wall,  but  soon  its  nucleus  and  proto- 


354  EVOLUTION  AND  ANIMAL  LIFE 

plasm  begin  to  break  up  by  repeated  division  (the  parts  all 
being  held  together,  however,  in  the  wall  of  the  zygote),  and 
by  the  end  of  the  twelfth  or  fourteenth  day  the  zygote's  proto- 
plasm may  have  become  divided  into  ten  thousand  minute 
sporozoites.  The  zygote  wall  now  breaks  down,  thus  releasing 
the  thousands  of  active  little  sporozoites  into  the  general  body 
cavity  of  the  mosquito.  This  cavity  is  filled  with  flowing 
blood  plasm — insects  do  not  have  a  closed  but  an  almost  com- 
pletely open  circulatory  system — and  swimming  about  in  this 
plasm  the  sporozoites  soon  make  their  way  forward  and  into 
the  salivary  glands  of  the  moscjuito.  Now  when  the  insect 
pierces  a  human  being  to  suck  blood,  it  injects  a  certain  amount 
of  salivary  fluid  into  the  wound  (presumably  to  keep  the  blood 
from  clotting  at  the  puncture)  and  with  this  fluid  go  many  of 
the  sporozoites.  Thus  a  new  infection  of  malaria  is  made. 
The  sporozoites  may  lie  in  the  salivar}^  glands  for  several  weeks, 
and  so  for  the  whole  time  from  twelve  to  fourteen  days  after 
the  mosquito  has  become  infected  with  the  malarial  parasite 
by  sucking  blood  from  a  malarial  patient  until  the  sporozoites 
in  the  salivary  glands  finally  die,  it  is  a  means  of  the  dissemina- 
tion of  the  disease.  There  can  be  no  malaria  without  mos- 
quitoes to  propagate  and  disseminate  it,  and  yet  no  mosquitoes 
can  propagate  and  disseminate  malaria  without  having  access 
to  malarial  patients.  The  only  mosquito  species  in  this  country 
which  has  been  proved  to  be  a  malaria  disseminator  is  Anoph- 
eles viaculijpennis ,  a  spotted- winged  form  spread  OA^er  the 
whole  continent.- 

In  the  great  branch  or  phylum  of  flatworms  (Platyhelmin- 
thes),  that  group  of  animals  which  of  all  the  principal  animal 
groups  is  widest  in  its  distribution,  perhaps  a  majority  of  the 
species  are  parasites.  Instead  of  being  the  exception,  the 
parasitic  life  is  the  rule  among  these  w^orms.  Of  the  three 
classes  into  w^iich  the  flatworms  are  divided,  almost  all  of  the 
members  of  two  of  the  classes  are  parasites.  The  common 
tapeworm  (Tcenia)  (Fig.  212),  which  lives  parasitically  in  the 
intestine  of  man,  is  a  good  example  of  one  of  these  classes. 
It  has  the  form  of  a  narrow  ribbon,  which  may  attain  the 
length  of  several  yards,  attached  at  one  end  to  the  w^all  of  the 
intestine,  the  remainder  hanging  freely  in  the  interior.  Its 
body  is  composed  of  segments  or  serially  arranged  parts,  of 
which  there  are  about  eight  hundred  and  fifty  altogether.     It 


r>AR.\SITISM   AND   DEGEXEllATIOX 


35.' 


o 


has  no  mouth  nor  uhmcntary  canaL  It  fccils  sinii)ly  Ijy  ab- 
sorbing into  its  body,  through  tlie  surface,  tlio  nutritious, 
ah-eady  digested  hc^uid  food  in  the  intestine'.  '^J'here  are  no 
eyes  nor  other  special  sense  organs,  nor  any  oi-gans  of  locomo- 
tion. The  l:)ody  is  very  degenerate.  The  hfe  history  of  tlie 
tapeworm  is  interesting,  because  of  tlie  necessity  of  two  hosts 
for  its  completion.  The  eggs  of  the  ta])eworm  ])ass  from  the 
intestine  with  the  excreta,  and  must  be  taken  into  the  body 
of  some  other  animal  iiu  order  to  de- 
velop. In  tiie  case  of  one  of  the  several 
species  of  tapeworms  that  infest  man, 
this  other  host  must  be  the  ])ig.  In 
the  ahmentary  canal  of  the  j)ig  the 
young  tapeworm  develops  and  later 
bores  its  way  through  the  walls  of  the 
canal  and  becomes  imbedded  in  the 
muscles.  There  it  lies,  until  it  finds  its 
way  into  the  alimentary  canal  of  man 
by  his  eating  the  flesh  of  the  pig.  In 
the  intestine  of  man  the  tapeworm  con- 
tinues to  develop  until  it  becomes  full 


grown. 


Fig.  212. — T.npeworm, 
TivniasoUutn.  In  the 
m)per  Icft-haiul  cor- 
ner is  the  much  en- 
larged licail.  (After 
Leuckart.) 


In  a  lake  in  Yellowstone  Park  the 
suckers  are  infested  by  one  of  the  flat- 
worms  {Ligida)  that  attains  a  size  of 
nearly  one  fourth  the  size  of  the  fish  in 
whose  intestines  it  lives.  If  the  tape- 
worm of  man  attained  such  a  compara- 
tive size,  a  man  of  two  hundred  pounds'  weight  would  lie  in- 
fested by  a  parasite  of  fifty  ])ounds'  weight. 

Another  group  of  animals,  many  of  whose  members  are 
parasites,  are  the  roundworms  or  threadworms  (Xemathel- 
minthes).  The  free-living  roundworms  are  active,  well- 
organized  animals,  but  the  parasitic  kinds  all  sliow  a  greater 
or  less  degree  of  degeneration.  One  of  the  most  terrible  para- 
sites of  man  is  a  roundworm  called  TricJiiun  spiralis  (Fig.  2Ki). 
It  is  a  minute  worm,  from  one  to  three  millimeters  long,  which 
in  its  adult  condition  lives  in  the  intestine  of  man  or  of  the  pig 
or  other  mammals.  The  young  are  born  alive  and  bore  through 
the  walls  of  the  intestine.  They  migrate  to  the  voluntary 
muscles  of  the  hosts,  especially  those  of  the  limbs  and  back, 


356 


EVOLUTION  AND  ANIMAL  LIFE 


and  here  each  worm  coils  itself  up  in  a  muscle  fiber  and  becomes 
inclosed  in  a  spindle-shaped  cyst  or  cell  (Fig.  213)/  A  single 
muscle  may  be  infested  by  hundreds  of  thousands  of  these 
minute  worms.  It  has  been  estimated  that  fully  one  hundred 
miUion  encysted  worms  may  exist  in  the  muscles  of  a  '^  trichin- 
ized'^  human  body.  The  muscles  undergo  more  or  less  de- 
generation, and  the  death  of  the  host  may  occur.    It  is  necessary, 

for  the  further  development  of  the 
worms,  that  the  flesh  of  the  host  be 
eaten  by  another  mammal,  as  the 
flesh  of  the  pig  by  man,  or  the  flesh 
of  man  by  a  pig  or  rat.  The  Trichince 
in  the  alimentary  canal  of  the  new 
host  develop  into  active  adult  worms 
and  produce  new  young. 

In  the  Yellow^stone  Lake  the  trout 
are  infested  by  the  larvse  or  young  of 
a  roundworm  {Bothriocephalus  cordi- 
ceps)  which  reach  a  length  of  twenty 
inches,  and  which  are  often  found 
stitched,  as  it  were,  through  the  vis- 
cera and  the  muscles  of  the  fish.  The 
infested  trout  become  feeble  and  die, 
or  are  eaten  by  the  pelicans  which  fish 
in  this  lake.  In  the  alimentary  canal 
of  the  pelican  the  worms  become 
adult,  and  parts  of  the  worms  con- 
taining eggs  escape  from  the  ali- 
mentary canal  with  the  excreta.  These 
portions  of  worms  are  eaten  by  tJie  trout,  and  the  eggs  give 
birth  to  new  worms  which  develop  in  the  bodies  of  the  fish 
with  disastrous  effects.  It  is  estimated  that  for  each  pelican 
in  Yellowstone  Lake  over  five  million  eggs  of  the  parasitic 
worms  are  discharged  into  the  lake. 

The  young  of  various  carnivorous  animals  are  often  infested 
by  one  of  the  species  of  roundworms  called  "  pup  worms " 
(Uncinaria) .  Recent  investigations  show  that  thousands  of 
the  young  or  pup  fur  seals  are  destroyed  each  year  by  these 
parasites.  The  eggs  of  the  worm  lie  through  the  winter  in  the 
sands  of.  the  breeding  grounds  of  the  fur  seal.  The  young 
receive  them  from  the  fur  of  the  mother  and  the  worm  de- 


FiG.  213. — Trichina  spiralis, 
the  terrible  parasite  of  pork: 
a,  Male;  6,  cyst;  c,  female. 


PARASITISM   AM)    DEGENERATION 


OOi 


veiops  in  tlic  ii])por  intostine.  It  feedrt  on  lliu  blood  of  the 
young  seal,  which  finally  dies  from  anemia.  On  the  sand 
beaches  of  the  seal  islands  in  I'lcring  Sea  th("r(>  iire  every  year 


■% 


4 
if 


^» 


^ 


1^J 


u 
0 


-  "2 

r     S 
—    y. 


O 


r     3 


"_     3 

Z  2 

1-  -J 


-* 
5 


*-- 


1 


U^ 


thousands  of  dead  seal  pups  which  have  been  killed  by  this 
parasite  (Fig.  214).  On  the  rocky  rookeries,  the  young  seals 
are  not  affected  by  this  parasite. 


358 


EVOLUTION  AND  ANIMAL  LIFE 


Among  the  more  highly  organized  animals  the  results  of  a 
parasitic  life,  in  degree  of  structural  degeneration,  can  be  more 
ieadily  seen.  A  well-known  parasite,  belonging  to  the  Crus- 
tacea— the  class  of  shrimps,  crabs,  lobsters,  and  crayfishes — is 
Sacculina.  The  young  Sacculiiia  (Fig.  215,  A)  is  an  active,  free- 
swimming  larva  much  like  a  3^oung  prawn  or  young  crab.  But 
the  adult  bears  absolutely  no  resemblance  to  such  a  typical 
crustacean  as  a  crayfish  or  crab.     The  Sacculina  after  a  short 


c\g.  215. — Development  of  the  parasitic  crustacean,  Sacculina  ccrcinus:  A,  Naplius 
stage; \B,  cypris  stage;  C,  adult  attached  to  its  host,  the  crab,  Carcinus  mccnas. 
(After  Hertwig.) 


period  of  independent  existence  penetrates  to  the  abdomen  of  a 
crab,  and  completes  its  development  while  living  as  a  parasite  on 
the  crab.  In  its  adult  condition  (Fig.  215,  C)  it  is  simply  a  great 
tumorlike  sac,  bearing  many  delicate  rootlike  suckers  which 
penetrate  the  body  of  the  crab  host  and  absorb  nutriment. 
The  Sacculina  has  no  eyes,  no  mouth  parts,  no  legs,  or  other 
appendages,  and  hardly  any  of  the  usual  organs  except  re- 
productive organs.     Degeneration  here  is  carried  ver}^  far. 

Other  parasitic  Crustacea,  as  the  numerous  kinds  of  fish 
lice  (Fig.  216)  which  live  attached  to  the  gills  or  to  other  parts 
of  fish,  and  derive  all  their  nutriment  from  the  body  of  the 
fish,  show  various  degrees  of  degeneration.  With  some  of 
these  fish  lice  the  female;  which  looks  like  a  puffed-out  worm, 
is  attached  to  the  fish  or  other  aquatic  animal,  while  the  male, 
which  is  perhaps  only  a  tenth  of  the  size  of  the  female,  is  per- 
manently attached  to  the  female,  living  parasitically  on  her. 


P.\RASIT1SM    AND    DEGENERATION' 


359 


I'^io.  216.— The  fixh  louse. 
LerncEcera:  a,  Adult;  6, 
lar\'a. 


Among  the  insects  there  are  many  kinds  that  live  para- 
sitically  for  part  of  their  life,  and  not  a  few  that  live  as 
parasites  for  their  wliolc  life.  The  true 
sucking  lice  and  the  l)ird  lice  live  for 
their  whole  Uves  as  external  ])arasites 
on  the  bodies  of  their  host,  but  they 
are  not  fixed — that  is,  they  retain  their 
legs  and  i)ower  of  locomotion,  although 
they  have  lost  their  wings  through  de- 
generation. The  eggs  of  the  lice  are 
deposited  on  the  hair  of  the  mammal 
or  bird  that  serves  as  host;  the  young 
hatch  and  immediately  begin  to  live  as 
parasites,  eitlier  sucking  the  bloo'l  or 
feeding  on  the  hair  or  feathers  of  the 
host.  In  the  order  Hymeno})tera  there 
are  several  families,  all  of  whose  mem- 
bers live  during  their  larval  stage  as  parasites.  We  may 
call  all  these  hymenopterous  })arasites  ichneumon  flies.  The 
ichneumon  flies  are  parasites  of  other  insects,  especially  of  the 

larvae  of  beetles  and  moths  and  l)Utter- 
fiies.  In  fact,  the  ichneumon  flies  do 
more  to  keej)  in  check  the  increase  of  in- 
jurious and  destructive  cateri)illars  than 
do  all  our  artificial  remedies  for  these  in- 
sect pests.  The  adult  ichneumon  fly  is 
four-winged  and  lives  an  active,  indepen- 
dent life.  It  lays  its  eggs  either  in  or  on 
or  near  some  caterpillar  or  beetle  grub, 
and  the  young  ichneumon,  when  hatchetl. 
burrows  into  the  body  of  its  host,  feed- 
ing on  its  tissues,  but  not  attacking  such 
organs  as  the  heart  or  nervous  ganglia, 
whose  injury  might  mean  inunediate  death 
to  the  host.  The  caterj)illar  lives  with  the 
ichneumon  grub  within  it,  usually  luitil 
nearly  time  for  its  jnipation.  Jn  many 
inst;tnces,  indeed,  it  pupates  with  the 
parasite  still  feeding  within  its  bodw  but  it  never  comes  to 
maturity.  The  larval  ichneumon  fly  i^upates  either  within  the 
body  of  its  host  (Fig.  218)  or  in  a  tiny  silken  cocoon  outside 


Fig.  217. — The  ichneu- 
mon fly,  Pimpla  ccn- 
quisitor,  laying  eggs 
in  the  cocoon  of  the 
American  tent  cater- 
pillar moth.  CAftor 
Fiske;  about  natural 
size.) 


360  EVOLUTION   AND   ANIMAL   LIFE 

of  its  body.  From  the  cocoons  the  adult  winged  ichneumon 
flies  emerge^  and  after  mating  find  another  host  on  whose 
body  to  lay  their  eggs. 

One  of  the  most  remarkable  ichneumon  flies  is  Thalessa 
(Fig.  219),  which  has  a  A^ery  long,  slender,  flexible  ovi- 
positor, or  egg-laying  organ.  An  insect  known  as  the  pigeon 
horntail  (Tremex  columba)  (Fig.  220)  deposits  its  eggs,  by 
means  of  a  strong,  piercing  ovipositor,  half  an  inch  deep  in 
the  trunk  wood  of  growing  trees.  The  young  or  larval  Tremex 
is  a  soft-bodied  white  grub,  which  bores  deeply  into  the  trunk 
of  the  tree,  filling  up  the  burrow  behind  it  wdth  small  chips. 
The  Thalessa  is  a  parasite  of  the  Tremex,  and  "when  a  female 
Thalessa  finds  a  tree  infested  by  Tremex,  she  selects  a  place 


Fig.  218. — Parasitized  caterpillar  from  which  the  ichneumon  fly  parasites  have  issued, 

showing  circular  holes  of  escape  in  skin. 

which  she  judges  is  opposite  a  Tremex  burrow,  and,  elevating 
her  long  ovipositor  in  a  loop  over  her  back,  with  its  tip  on  the 
bark  of  the  tree  (Fig.  221),  she  makes  a  derrick  out  of  her  body 
and  proceeds  with  great  skill  and  precision  to  drill  a  hole  into 
the  tree.  When  the  Tremex  burrow  is  reached  she  deposits 
an  egg  in  it.  The  larva  that  hatches  from  this  egg  creeps 
along  this  burrow  until  it  reaches  its  victim,  and  then  fastens 
itself  to  the  horntail  larva,  which  it  destroys  by  sucking  its 
blood.  The  larva  of  Thalessa,  when  full  grown,  changes  to 
a  pupa  within  the  burrow  of  its  host,  and  the  adult  gnaws 
a  hole  out  through  the  bark  if  it  does  not  find  the  hole  already 
made  by  the  Tremex.^' 

The  beetles  of  the  family  Stylopidse  present  an  interesting 
case  of  parasitism.  The  adult  males  are  winged,  but  the  adult 
females  are  wingless  and  grublike.  The  larval  stylopid  at- 
taches itself  to  a  wasp  or  a  bee,  and.  bores  into  its  abdomen. 
It  pupates  within  the  abdomen  of  the  wasp  or  bee,  and  lies 
there  with  its  head  projecting  slightly  from  a  suture  between 
two  of  the  body  rings  of  its  host. 


1>ARASITISM   AND   DEGENERATION 


3G1 


Almost   all  of  the   mites  and   ticks,   animals  allied   to  the 
spiders,  hve  parasitieally.     Most  of  them  live  as  external  jxira- 
sites,  siiekinoj  the  blood  of  their   liost,   l)ut   some  live  under- 
neath the  skin   like  the  itch 
mite§  (Fig.  222),  which  cause, 
in   man,   the   disease    known 
as  the  itch. 

Among  the  vertebrate  ani- 
mals there  are  not  many  ex- 
amples of  true  parasitism. 
The  hagfishes  or  borers 
(Myxine,  etc.)  have  been  al- 
ready mentioned.  These  are 
long  and  cylindrical,  eellike 
creatures,  very  slimy  and 
very  low  in  structure.  The 
mouth  is  without  jaws,  but 
forms  a  sucking  disk,  by 
which  the  hagfish  attaches 
itself  to  the  body  of  some 
other  fish.  By  means  of  tlic 
rasping  teeth  on  its  tongue, 
it  makes  a  round  hole 
through  the  skin,  usually  at 
the  throat.  It  then  devours 
all  the  muscular  "substance 
of  the  fish,  leaving  the  vis- 
cera untouched.  When  the 
fish  finally  dies  it  is  a  mere 
hulk  of  skin,  scales,  l)ones, 
and  viscera,  nearly  all  the 
muscle  being  gone.  Then 
the  hagfish  slips  out  and  at- 
tacks another  individual. 

The  lamprey,  another  low 
fish,  in  similar  fashion   feeds  leechlike  on   the  blood  of  other 
fishes,  which   it  obtains   l)y  hicerating  the  flesh  with  its  ras|>- 
hke  teeth,  remaining  attached   by  tlie  round  sucking  disk  of 
its  mouth. 

Certain  birds,  as  the  cowbii-d   and  the   Kurojiean  cuckoo, 
have  a  parasitic  habit,  laying  their  eggs  in  the  nests  of  other 


Fig.  219. — The  larjre  ichneumon  fly, 
Thalessd,  with  long  ovipositor. 


362 


EVOLUTION  AND  ANIMAL  LiFiG 


Fig.     220. — The    pigeon    horn-tail,    Tremex 
columha,  with  strong  bearing  ovipositor. 


birds,  leaving  their  young  to  be  hatched  and  reared  by  their 
umviUing  hosts.     This  is,  however,  not  bodily  parasitism,  such 

as    is    seen    among     lower 
forms. 

We  may  also  note  ^that 
parasitism  and  consequent 
structural  degeneration  are 
not  at  all  confined  to  ani- 
mals. Many  plants  are 
parasites  and  show  marked 
degenerative  characteristics. 
The  dodder  is  a  familiar 
example,  clinging  to  living 
green  plants  and  thrusting 
its  haustoria  or  rootlike 
suckers  into  their  tissue  to 
draw  from  them  already 
elaborated  nutritive  sap.  Many  fungi  like  the  rusts  of  cereals, 
the  mildew  of  roses,  etc.,  are  parasitic.  Numerous  plants,  too, 
are  parasites,  not  on  other  plants,  but  on  animals.  Among 
these  are  the  hosts 
of  bacteria  (sim- 
plest of  the  one- 
celled  plants)  that 
swarm  in  the  tis- 
sues of  all  animals, 
some  of  which  are 
causal  agents  of 
some  of  the  worst 
of  human  and  ani- 
mal diseases  (as 
typhoid  fever,  diph- 
theria, and  cholera 
in  man,  anthrax  in 
cattle).  There  'are 
also  many  more 
highly     organized 

fungi  like  the  whole  family  of  Entomophthor^e,  and  the  genus 
SporotrichiLm  that  live  in  and  on  the  bodies  of  insects,  often 
killing  them  by  myriads.  One  of  the  great  checks  to  the 
ravages  of  the  corn  and  wheat-infesting  chinch  bug  {BlisstiB 


Fig.  221. — Thalessa  lunator  boring.     (After  Comstock.) 


PARASITISM   AND   DEGENERATION 


363 


leiLcopterus)  of  the  Mississippi  Valley  is  a  parasitic  fungus  (Sporo- 
trichum  glob idijer urn).  In  the  autumn,  house  flies  may  often 
be  seen  dead  against  a  windowpane  surrounded  by  a  delicate 


ring    or    halo    of    white. 


This    ring   is 


composed  of  spores  of  the  fungus,  Em- 
pnsa  aphidis,  which  has  grown  through 
all  the  tissues  of  tlie  flv  wliile  alive, 
finally  resulting  in  its  death.  The 
spores  are  thrown  off  from  tiny  fruit- 
ing hypha)  of  the  fungus  which  have 
grown  out  through  the  body  wall  of 
the  insect.  And  they  serve  to  inocu- 
late other  flies  that  may  come  near. 

Just  as  in  animals,  so  in  })lants; 
parasitic  kinds,  especially  among  the 
higher  groups  as  the  flowering  j^lants, 
often  show  marked  degeneration.  Leaves 
may  be  reduced  to  mere  scales,  roots  are  lost,  and  the  water- 
conducting  tissues  greatly  reduced.  This  degeneration  in  plants 
naturally  affects  primarily  those  parts  which  in  the  normal 
plant  are  devoted  to  the  gathering  and  elaboration  of  inor- 
ganic food  materials,  namely,  the  leaves  and  stems  and  roots. 


Fig.  222.— The  itch  mite, 
Sarcoptcs  acabeu 


Fig.  223. — The  fungus,  Cordiceps,  growing  on  a  caterpillar.     (Natural  size.) 


The  flowers  or  reproductive  organs  usually  retain,  in  parasites, 
all  of  their  high  development. 

While  parasitism  is  the  principal  cause  of  degeneration  of 
animals,  other  causes  may  be  also  concerned.  Fixed  animals 
or  animals  leading  inactive  or  sedentary  lives,  also  become 
degenerate,  even  when  no  parasitism  is  concerned.  The  tuni- 
cata  or  s'^a  squirts  (Fig.  224)  are  animals  whose  simplicity  of 
structure  is  due  to  degeneration  from  the  acquisition  of  a 
sedentary  habit  of  life. 

The  young  or  larval  tunicate  is  a  free-swinuning  active  tad- 
polelikc  creature  with  organs  much  like  those  of  the  adult  of 


364 


EVOLUTION   AND   ANIMAL   LIFE 


the  simplest  fishes  or  fishUke  forms.  That  is,  the  sea  squirt 
begins  hfe  as  a  primitively  simple  vertebrate.  It  possesses 
in  its  larval  stage  a  notochord,  the  delicate  structure  which 
precedes  the  formation  of  a  backbone,  extending  along  the 
upper  part  of  the  body,  below  the  spinal  cord.  It  is  found 
in  all  young  vertebrates,  and  is  characteristic  of  the  branch. 

The  other  organs  of  the 
young  tunicate  are  all  of 
vertebral  type.  But  the 
young  sea  squirt  passes 
a  period  of  active  and 
free  life  as  a  little  fish, 
after  which  it  settles  down 
and  attaches  itself  to  a 
stone  or  shell  or  wooden 
pier  by  means  of  suckers, 
and  remains  for  the  rest 
of  its  life  fixed.  Instead 
of  going  on  and  develop- 
ing into  a  fishlike  creature, 
it  loses  its  notochord,  its 
special  sense  organs,  and 
other  organs;  it  loses  its 
complexity  and  high  or- 
ganization and  becomes, 
a  "mere  rooted  bag 
with  a  double  neck,"  a 
thoroughly  degenerate 
animal. 
A  barnacle  is  another  example  of  degeneration  through 
quiescence.  The  barnacles  are  crustaceans  related  most 
nearly  to  the  crabs  and  shrimps.  The  young  barnacle  just 
from  the  egg  (Fig.  225,  /)  is  a  six-legged,  free-swimming 
nauplius,  much  like  a  young  shrimp,  with  single  eye.  In 
its  next  larval  stage  it  has  six  pairs  of  swimming  feet,  and 
two  large  antennae  or  feelers,  and  still  lives  an  independent, 
free-swimming  life.  When  it  makes  its  final  change  to  the 
adult  condition,  it  attaches  itself  to  some  stone  or  shell,  or 
pile  or  ship's  bottom,  loses  its  feelers,  develops  a  protecting 
shell,  and  gives  up  all  power  of  locomotion.  Its  swim- 
ming   feet    become    changed    into    grasping    organs,    and    it 


■fe.^U 


Fig.  224. — The  sea  squirt  or  tunicate. 


PARASITISM   AND   DEGENERATION 


365 


loses  most  of  its  outward  resemblances  to  the  other  members 
of  its  class  (Fig.  225,  e). 

Certain  insects  live  sedentary  or  fixed  lives.  All  the  mem- 
bers of  the  family  of  scale  insects  (Coccida;),  in  one  sex  at 
least,  show  degeneration  that  has  l)een  caused  by  (juiescence. 
One  of   these    coccids,   called    the   red   orange  scale,  is  very 


Fig.  225, — Three  crustaceans  and  their  Farvrr :  a,  Prawii,  Pcneus;  b,  Pennia,  larva; 
c,  Sacculina,  parasite;  d,  larva  Sacculina;  e,  barnacle,  Lepas,  quiescent;  /.  larva 
of  barnacle.     (After  Haeckel.) 


abundant  in  Florida  and  California  and  in  other  orange-grow- 
ing regions.  Tlie  male  is  a  beautiful,  tiny,  two-wingetl  midge, 
but  the  female  is  a  wingless,  footless  little  sac  without  eyes  or 
other  organs  of  special  sense,  and  lies  motionless  under  a 
flat,  thin,  circular,  reddish  scale  composed  of  wax  and  two 
or  three  cast  skins  of  the  insect  itself.  The  insect  has  a  long, 
slender,  flexible,  sucking  beak,  which  is  thrust  into  the  leaf  or 
stem  or  fruit  of  the  orange  on  which  tlie  "scale  bug"  lives  and 
througli  which  tlie  insect  sucks  the  orange  sap,  which  is  its  only 
food.    It  lays  eggs  or  gives  birth  to  young  under  its  body,  under 


366 


EVOLUTION   AND  ANIMAL   LIFE 


the  protecting  wax  scale,  and  dies.  From  the  eggs  hatch  active 
Uttle  larval  scale  bugs  with  eyes  and  feelers  and  six  legs.  They 
crawl  from  under  the  wax  scale  and  roam  about  over  the  orange 
tree.  Finally,  they  settle  down,  thrust  their  sucking  beak 
into  the  plant  tissues,  and  cast  their  skin.  The  females  lose 
at  this  molt  their  legs  and  eyes  and  feelers.     Each  becomes  a 

mere  motionless  sac  capable 
only  of  sucking  up  sap  and 
of  laying  eggs.  The  young 
males,  however,  lose  their 
sucking  beak  and  can  no 
longer  take  food,  but  they 
gain  a  pair  of  wings  and  an 
additional  pair  of  eyes.  They 
fly  about  and  fertilize  the 
saclike  females,  which  then 
molt  again  and  secrete  the 
thin  wax  scale  over  them. 

Throughout  the  animal 
kingdom  loss  of  the  need 
of  movement  is  followed 
by  the  loss  of  the  power 
to  move,  and  of  all  struc- 
tures related  to  it. 

Loss  of  certain  organs 
may  occur  through  other 
causes  than  parasitism  and 
a  fixed  hfe.  Man}^  insects 
live  but  a  short  time  in 
their  adult  stage.  May  flies 
live  for  but  a  few  hours  - 
or,  at  most,  a  few  da3^s.  They  do  not  need  to  take  food  to 
sustain  life  for  so  short  a  time,  and  so  their  mouth  parts  have 
become  rudimentary  and  functionless  or  are  entirely  lost. 
This  is  true  of  some  moths  and  numerous  other  specially  short- 
lived insects.  Among  the  social  insects  the  workers  of  the 
termites  and  of  the  true  ants  are  wingless,  although  they  are 
born  of  winged  parents,  and  are  descendants  of  winged  ancestors. 
The  modification  of  structure  dependent  upon  the  division  of 
labor  among  the  individuals  of  the  community  has  taken  the 
form,  in  the  case  of  the  workers,  of  a  degeneration  in  the  loss  of 


Pig.  226. — The  black  scale,  LecaniuTti  olece', 
and  its  parasite,  the  tiny  chalcid  fly,  Scu- 
tellista  cyanea;  and  the  ladybird  beetle, 
Rhizobius  ventralis.     (After  Isaacs.) 


PARASITISM   AND   DEGENERATION  %7 

the  wings.  Insects  that  hvc  in  caves  are  mostly  Wind;  tliey 
have  lost  the  eyes,  whose  function  could  not  be  exercised  in  the 
darkness  of  the  cave.  Certain  island-inhabiting  insects  have 
lost  their  wings,  flight  being  attended  with  too  much  danger. 
The  strong  sea  breezes  may  at  any  time  carry  a  flying  insect 
off  the  small  island  to  sea.  Probably  only  those  which  do  not 
fly  much  survive,  and  so  by  natural  selection  wingless  l)reeds 
or  species  are  produced.  Finally,  we  may  mention  the  great 
modifications  of  structure,  often  resulting  in  the  loss  of  certain 
organs,  which  take  place  to  produce  protective  resemblances 
(see  Chapter  XIX).  In  such  cases  the  body  may  be  modified 
in  color  and  shape  so  as  to  resemble  some  part  of  the  environ- 
ment, and  thus  the  animal  may  be  unperceived  by  its  enemies. 
Many  insects  have  lost  their  wings  through  this  cause. 

¥/hen  we  say  that  a  parasitic  or  quiescent  mode  of  lif(^  leads 
to  or  causes  degeneration,  we  have  explained  the  stimulus  or 
the  ultimate  reason  for  the  degenerative  changes,  but  we  have 
not  shown  just  how  parasitism  or  cpiiescence  actually  j)roduces 
these  changes.  Degeneration  or  the  atrophy  and  disaj)pear- 
ance  of  organs  or  parts  of  a  body  is  often  said  to  be  due  to  dis- 
use. That  is,  the  disuse  of  a  part  is  believed  by  many  natural- 
ists to  be  the  sufficient  cause  for  its  gradual  dwindling;  and  final 
loss.  That  disuse  can  so  affect  parts  of  a  body  during  the  life- 
time of  an  individual  is  true.  A  muscle  unused  becomes  soft 
and  flabby  and  small.  Whether  the  effects  of  such  disuse  can 
be  inherited,  however,  is  open  to  serious  doubt.  Sucli  in- 
heritance must  be  assumed  if  disuse  is  to  account  for  the  gradual 
growing  less  and  final  disappearance  of  an  organ  in  tlu*  course 
of  many  generations.  Some  naturalists  believe  that  the  results 
of  such  disuse  can  be  inherited,  but  as  yet  such  belief  rests  on 
no  certain  knowledge.  If  characters  accpiired  during  the  lifi^ 
time  of  the  individual  are  subject  to  inheritance,  disuse  alone 
may  explain  degeneration.  If  not,  some  other  innnediate 
cause,  or  some  other  cause  along  with  disuse,  must  be  found. 

We  are  accustomed,  perhaps,  to  think  of  tlegeneration  as 
necessarily  implying  a  disadvantage  in  life.  A  degenerate 
animal  is  considered  to  be  not  the  equal  of  a  nondegenerate 
animal,  and  this  would  be  true  if  both  kinds  of  animals  had  to 
face  the  same  conditions  of  life.  The  blind,  footless,  simple, 
degenerate  animal  could  not  coj)e  witli  tiie  active,  keen-sighted, 
highly  organized  nondegenerate  in  free  competition.     Hut  free 


368  EVOLUTION  AND  ANIMAL   LIFE 

competition  is  exacth^  what  the  degenerate  animal  has  nothing 
to  do  with.  Certainly  the  Sacculina  lives  successfully;  it  is 
well  adapted  for  its  own  peculiar  kind  of  life.  For  the  life  of  a 
scale  insect,  no  better  type  of  structure  could  be  devised.  A 
parasite  enjoys  certain  obvious  advantages  in  life,  and  even 
extreme  degeneration  is  no  drawback,  but  rather  favors  it  in 
the  advantageousness  of  its  sheltered  and  easy  life.  As  long 
as  the  host  is  successful  in  eluding  its  enemies  and  avoiding 
accident  and  injury,  the  parasite  is  safe.  It  needs  to  exercise 
no  activity  or  vigilance  of  its  own;  its  life  is  easy  as  long  as  its 
host  lives.  But  the  disadvantages  of  parasitism  and  degenera- 
tion are  apparent  also.  The  fate  of  the  parasite  is  usually 
bound  up  with  the  fate  of  the  host.  When  the  enemy  of  the 
host  crab  prevails,  the  Sacculina  goes  down  without  a  chance  to 
struggle  in  its  own  defense.  But  far  more  important  than 
the  disadvantage  in  such  particular  or  individual  cases  is  the 
disadvantage  of  the  fact  that  the  parasite  cannot  adapt  itself 
in  any  considerable  degree  to  new  conditions.  It  has  become 
so  specialized,  so  greatly  modified  and  changed  to  adapt  itself 
to  the  one  set  of  conditions  under  which  it  now  lives,  it  has 
gone  so  far  in  its  giving  up  of  organs  and  body  parts,  that  if 
present  conditions  should  change  and  new  ones  come  to  exist, 
the  parasite  could  probably  not  adapt  itself  to  them.  The 
independent,  active  animal  with  all  its  organs  and  all  its  func- 
tions intact,  holds  itself,  one  may  say,  ready  and  able- to  adapt 
itself  to  any  new  conditions  of  life  which  may  gradually  come 
into  existence.  The  parasite  has  risked  everything  for  the 
sake  of  a  sure  and  easy  life  under  the  presently  existing  con- 
ditions.    Change  of  conditions  means  its  extinction. 


CHAPTER   XVIII 

MUTUAL   AID    AND    COMMUNAL    LIFE    AMONG 

ANIMALS 

More  ancient  than  competition  is  conil^ination.  The  little  feeble 
fluttering  folk  of  God,  the  spinning;  insects,  the  little  mice  in  the 
meadow,  the  rat  in  the  cellar,  the  crane  in  the  marshes  or  the  boominor 
bittern,  all  these  have  learned  that  God's  "greatest  word  is  tofccther 
and  not  alone.  He  who  is  striving  to  make  God's  blessing  and  bounty 
possible  to  most  is  stepping  into  line  ^vith  nature.  The  selfish  man  is 
the  isolated  man. — Oscar  Carlton  McCulloch. 

Man  is  not  the  only  social  animal,  nor  the  only  animal 
species  whose  individuals  live  in  mutually  advantageous  rela- 
tions with  each  other,  and  in  mutually  advantageous  relations 
with  individuals  of  other  animal  kinds.  Just  as  man  lives 
communally  and  mutually  helpfully  with  other  men,  so  do  the 
members  of  a  great  honeybee  or  ant  connnunity  live  together: 
and  as  we  find  various  other  animals  as  dogs,  horses,  and  doves 
living  under  the  care  and  protection  of  man  and  returning  to 
him  a  measure  of  service  in  work,  companionship,  or  other 
heli)fulness  for  his  care  and  feeding,  so  do  we  know  of  hundreds 
of  kinds  of  other  insects  that  live  commensally  with  ants,  each 
party  to  this  commensal  or  synil)iotic  life  gaining  something 
from  ^nd  giving  something  to  the  other  i)arty  of  this  arrange- 
ment. Indeed,  the  communal  bfe  of  such  insects  as  the  social 
bees,  wasps,  and  ants  is  developed  along  true  connnunistij 
lines  far  more  specialized  than  the  communism  shown  by  man. 

Just  as  students  of  human  society  can  trace  a  series  of  ste|)s 
from  a  very  primitive  living  together  or  communal  life  among 
men  to  the  present  highly  sjiecialized  condition,  so  among  vari- 
ous animals  we  can  find  a  long  series  of  gradatory  conditions  of 
social  life  from  mere  gregariousness  like  that  of  a  band  of  wolves 

3GD 


370  EVOLUTION   AND   ANIMAL   LIFE 

or  a  herd  of  bison,  to  the  extreme!}^  speciahzed,  interdependent 
and  unified  community  of  the  honeybee,  or  agricuhural  ant. 
Before  taking  up  this  series  of  stages  in  true  social  or  communal 
development  among  the  lower  animals,  however,  we  may  profit- 
ably give  some  attention  to  the  conditions  of  animal  association 
commonly  known  as  commensalism  or  symbiosis  in  which  in- 
dividuals of  one  species  are  associated  to  their  mutual  advan- 
tage with  individuals  of  different  species. 

In  the  relations  of  parasite  and  host,  discussed  in  the  last 
chapter,  all  the  advantages  of  the  association  lie  with  the  para- 
site. The  other  animal  involved,  the  host,  suffers  inconveni- 
ence, injury,  often  untimely  death.  But  in  commensalism  and 
symbiosis  both  associating  kinds  of  animals  reap  advantage,  or 


Fig.  227. — Remora    Echeneis  remora,  with  dorsal  fin  modified  to  be  the  sucking  plate 

by  which  the  fish  attaches  itself  to  a  shark. 

at  least  neither  suffers  in  any  serious  way  from  the  effects  of 
the  other's  presence.  The  two  kinds  live  together  in  harmony 
and  usually  to  their  actual  mutual  advantage.  The  term 
commensalism  may  be  applied  to  denote  a  condition  of  loose 
and  often  not  obviously  equally  mutual  advantageous  asso- 
ciation, while  symbiosis  is  used  to  refer  to  a  more  intimate  and 
persistent  association  with  maybe  marked  cooperation  and 
mutual  advantage.  A  few  examples  of  each  are  given  in  the 
following  pages.  Of  com*se,  no  marked  line  of  demarcation 
can  be  really  drawn  between  the  two  conditions,  any  more 
than  we  can  establish  a  sharp  distinction  between  the  preda- 
tory and  parasitic  modes  of  life. 

A  curious  example  of  commensalism  is  afforded  by  the 
different  species  of  Remoras  (Echenididse)  which  attach  them- 
selves to  sharks,  barracudas,  and  other  large  fishes  by  means 
of  a  sucking  disk  on  the  top  of  the  head  (Fig.  227).  This  disk 
is  made  by  a  modification  of  the  dorsal  fin.  The  Remora  thus 
attached  to  a  shark  may  be  carried  about  for  weeks,  leaving 
its  host  only  to  secure  food.    This  is  done  by  a  sudden  dash 


MUTUAL  AID  AND  COMMTTNAL   LIFE  AMONG  ANIMAL.S    371 

through  the  water.  The  Reniora  injures  llie  shark  in  no  way 
save,  perhaps,  by  the  shght  check  its  presence  gives  to  the 
shark's  speed  in  swimming. 

In  the  mouth  of  the  menhaden  (Brevoortia  tyratuius)  a  small 
crustacean  (Cynioihcu  prwgusUitor)  is  almost  always  ])resent, 
always  resting  in  the  front  of  the  lower  jaw.  This  arrange- 
ment is  of  advantage  to  the  crustacean,  but  is  a  matter  of  in- 
difference to  the  fish,  I^atrobe,  who  first  described  this  fish, 
compares  the  crustacean  to  the  pra>gustator  or  foret aster  of 
the  Roman  tyrants — a  slave  used  in  prevention  of  poisoning. 

Whales,  similarly,  often  carry  barnacles  about  with  them. 
These  barnacles  are  permanently  attached  to  the  skin  of  the 
whale  just  as  they  would  be  to  a  stone  or  wooden  pile.  Many 
small  crustaceans,  annelids,  moUusks,  and  other  invertebrates 
burrow  into  the  substance  of  living  sponges,  not  for  the  ])urpo^c 
of  feeding  on  them,  but  for  shelter.  On  the  other  hand,  the 
little  boring  sponge  (Cliotm)  burrows  in  the  shells  of  oysters 
and  other  bivalves  for  protection.  These  are  hardl\'  true  case.>3 
of  even  that  lesser  degree  of  mutualh'  advantageous  associa- 
tion which  we  are  calling  commensalism.  But  some  species  of 
sponge  "are  never  found  growing  except  on  the  baclvs  or  legs 
of  certain  crabs.''  In  these  cases  the  s])onge.  with  its  many 
plantlike  branches,  protects  the  crab  by  concealing  it  from 
its  enemies,  while  the  sponge  is  benefited  by  being  carried  al)out 
by  the  crab  to  new  food  supplies.  Certain  sponges  and  polyps 
are  always  found  growing  in  close  association,  though  what  the 
mutual  advantage  of  this  association  is  has  not  yet  been  foiuitl 
out. 

Among  the  coral  reefs  in  the  South  Seas  there  lives  an 
enormous  kind  of  sea  anemone  or  poly]^.  Individuals  of  this 
great  polyp  measure  two  feet  across  the  disk  when  fully  ex- 
panded. In  the  interior,  the  stomach  cavity,  which  com- 
municates freely  with  the  outside  \)y  means  of  the  large  mouth 
opening  at  the  free  end  of  the  polyp,  there  may  often  be  found 
a  small  fish  {Aj?iphi prion  pcrculn).  That  this  fish  is  j)urp()sely 
in  the  gastral  cavity  of  the  polyp  is  proved  by  the  fact  that 
when  it  is  dislodged  it  invariably  returns  to  its  singular  lodging 
place.  The  fish  is  brightly  colored,  being  of  a  brilliant  vermilion 
hue  with  three  broad  white  cross  bands.  The  discoverer  of, 
this  peculiar  habit  suggests  that  there  are  mutual  benefits  to 
fish  and  polyp  from  this  habit.     "The  fish  being  conspicuous, 


372 


EVOLUTION  AND  ANIMAL  LIFE 


is  liable  to  attacks,  which  it  escapes  by  a  rapid  retreat  into  the 
sea  anemone;  its  enemies  in  hot  pursuit  blunder  against  the 
outspread  tentacles  of  the  anemone  and  are  at  once  narcotized 
by  the  'thread  cells'  shot  out  in  innumerable  showers  from 

the  tentacles,  and  afterwards 
drawn  into  the  stomach  of  the 
anemone  and  digested.'' 

Small  fish  of  the  genus  N omens 
may  often  be  found  accompanj^- 
ing  the  beautiful  Portuguese 
man-of-war  {Physalia)  as  it  sails 
slowly  about  on  the  ocean's  sur- 
face (Fig.  228) .  These  little  fish 
lurk  underneath  the  float  and 
among  the  various  hanging 
threadlike  parts  of  the  Physalia, 
w^hich  are  provided  with  sting- 
ing cells.  The  fish  are  protected 
from  their  enemies  by  their  prox- 
imity to  these  stinging  threads. 
Similarly,  several  kinds  of  me- 
dusas are  known  to  harbor  or  to 
be  accompanied  by  the  young 
or  small  adult  fishes  {Caranx, 
P  series) . 

In  the  nests  of  the  various 
species  of  ants  and  termites 
many  different  kinds  of  other 
insects  have  been  found.  Some 
of  these  are  harmful  to  their 
hosts,  in  that  thev  feed  on  the 
food  stores  gathered  by  the  in- 
dustrious and  provident  ant,  but 
others  appear  to  feed  only  on 
refuse  or  useless  substances  in 
the  nest.  Some  appear  to  be  of  help  to  their  hosts  by  clean- 
ing the  nests  and  by  secreting  certain  fluids  much  liked  by 
the  ants.  Over  one  thousand  species  of  these  myrmecophilous 
(ant-loving)  and  termitophilous  (termite-loving)  insects  have 
been  recorded  by  collectors  as  living  habitually  in  the  nests  of 
ants   and  termites.     Many   of  them   (they  are   mostly   small 


Fig.  228. — The  Portuguese  man-of- 
war,  Physalia,  with  men-of-war 
fishes,  Nomeus  gronovii,  living  in 
the  shelter  of  the  stinging  feel^s. 
(Specimens  from  off  Tampa,  Fla.) 


MUTUAL  AID  AXD  COMMUNAL   LIFK   AMONG   AXIMAI-S    37.3 


> 


beetles  and  flics)  h.ave  lost  their  wings  and  have  had  their 
bodies  otherwise  considerably  modified,  usually  in  such  wise 
that  they  come  greatly,  to  resemble  in  external  ai)i)earance 
the  ants  with  w^hich  they  live.  The  owls  and  rattlesnakes 
which  hv3  with  the  prairie  dogs  in  their  villages  afford  another 
familiar  example  of  connncnsalism. 

Of  a  more  intimate  character,  and  of  more  obvious  anrl 
certain  mutual  advantage,  is  the  well-known  case  of  the  sym- 
biotic association  of  some  of  the  numerous  species  of  hermit 
crabs  and  certain  species  of  sea  anemones.  The  hermit  crab 
alwavs    takes    for 

its  habitation   the  "^r-     '",  '^j^/^jt. 

sliell     of     another  K  .  Hw . 

animal,  often  that 
of     the      common 
whelk.     All  of  the 
hind    part   of    the 
crab     hes      inside 
the  shell,  while  its 
head  with  its  great 
claws  project  from 
the  opening  of  the 
shell.    On  the  sur- 
face of    the  shell 
near  the  opening 
there  is  often  to 

be  found  a  hydroid  colony  (as  Fig.  220)  or  a  sea  anemone. 
The  last  is  fastened  to  the  shell  with  its  mouth  and  tentacles 
near  the  crab's  head.  The  sea  anemone  is  carried  from 
place  to  place  l)y  tlie  hermit  crab,  and  in  tliis  way  i.s 
much  aided  in  obtaining  food.  On  the  other  hand,  the 
crab  is  protected  from  its  enemies  by  {\\v  well-armed 
and  dangerous  tentacles  of  the  sea  anemone.  In  tlie 
tentacles  there  are  many  thousand  long,  slender  stinging 
threads,  and  the  fish  or  octopus  that  would  ol)tain  the  Iwr- 
mit  crab  for  food  must  first  deal  with  the  stinging  anemone. 
There  is  no  doubt  here  of  the  mutual  advantage  gained  by 
these  two  widely  different  but  intimately  associated  com- 
panions. If  the  sea  anemone  be  torn  away  from  the  shell 
inha])ited  by  one  of  these  cral)s,  the  cral)  will  wander  about, 
carefully  seeking  for  another  anemone.  When  it  finds  it,  it 
25 


Fig.  229. — Hermit  crab  within  a  shell  on  which  i:^  crowing 
a  colony  <jf  liy^lroi  I.s.  I'mlurorj/nc  canwa.  I'liis  roiony  is 
compose'l  of  sever:il  <li.Terenf  kinds  of  polyp  indivitluul.s, 
the  stinging  ones  being  situated  along  the  front  margin 
of  the  shell,     (.\fter  Weisrnann.) 


^74 


Evolution  and  animal  life 


struggles  to  loosen  it  from  its  rock  or  from  whatever  it  may 
be  growing  on,  and  does  not  rest  until  it  has  torn  it  loose  and 
placed  it  on  its  shell; 

There  are  numerous  small  crabs  called  pea  crabs  {Pin- 
notheres) which  live  habitually  insidfe  the  shells  of  living  mussels. 
The  mussels  and  the  crabs  tolerate  each  other,  perhaps  to  their 
mutual  benefit. 

The  relations  between  ants  and  aphids  (plant  lice)  are 
often  referred  to  in  popular  natural  histories  and  books  about 


Fig.  230. — The  hermit  crab,  Pagurus  hernhardus,  in  snail  shell  covered  with 

Hydractinia. 

insects  as  examples  of  symbiosis  of  unusual  interest.  Un- 
fortunately, however,  not  enough  cdreful  study  has  been  given 
to  many  of  these  apparently  true  examples  of  symbiosis  to 
enable  us  to  be  certain  of  the  truth  of  the  alleged  care  and 
guarding  of  the  ant-cows,  as  Linnaeus  called  these  aphids,  by 
their  milkers,  the  ants.  That  ants  do  swarm  about  the  aphids 
to  lap  up  the  "honey  dew"  excreted  by  them  is  wholly  true, 
and  the  very  presence  of  the  sharp- jawed  and  pugnacious 
ants  must  keep  away  many  enemies  of  the  defenseless  plant 
lice,  toothsome  morsels  for  the  ladybird  beetles,  fiower-fly 
larvae  and  other  predatory  insects. 

In  the  case  of  the  interesting  relations  between  the  corn 
root  aphid,  Aphis  maidisradici,  of  the  Mississippi  Valley  States 
and    the    little    brown    ant,    Lasius    hrunneus,    however,    we 


MUTUAL   AID   AND  COMMLNAJ.    1.11  I :    A.Mo.Nd   ANIMATES    375 

have  the  careful  ol^servations  of  Professor  lopbcs  to  rely  on. 
In  the  Mississipj)!  \'alley,  this  aphid  deposits  in  autumn  its 
eggs  in  the  ground  in  corn  fields,  often  in  tlie  galleries  of  the 
little  brown  ant.  The  following  spring  !)efore  the  corn  is 
planted,  these  eggs  hatch.  Now,  the  little  brown  ant  is  e<5- 
pecially  fond  of  the  honey  dew  secreted  by  the  corn  root  licr . 
So  when  the  latter  hatch  in  the  spring,  before  there  are  corn 
roots  for  them  to  fecMJ  on,  the  ants  carefully  j)lace  them  on 
the  roots  of  certain  kinds  of  grass  and  knotweed  {ScUiria, 
Polygonum) ,  and  there  protect  them  imtil  the  corn  germinates. 
They  are  then  removed  to  the  roots  of  the  corn.  It  is  j)rol)- 
ablc  that  the  ants  even  collect  the  eggs  of  the  a])hids  in  the 
autumn  and  carry  them  into  their  nests  for  ])rotection  and  can'. 

The  studies  of  Wheeler  and  others  have  revealed  some 
interesting  cases  of  the  living  together  of  different  species  of 
ants.  In  some  cases  one  of  the  ant  si)ecies  may  be  living  almost 
wholly  at  the  expense  of  the  other  species,  as  does  the  little 
yellow  thief-ant,  Solenopsis  rnoleMo.  Although  this  ant  some- 
times lives  in  independent  nests,  more  often  it  is  to  be  found 
living  in  association  with  some  large  ant  species — it  consorts 
with  many  different  hosts — feeding  almost  exclusively  on  the 
live  larva?  and  pupae  of  the  host.  The  thief-ant  is  so  small 
and  obscurely  colored  that  it  seems  to  live  in  the  nests  of  its 
host  practicall}^  unperceived.  The  Solcnopfiis  nest  may  be 
found  by  the  side  of  the  host  nest,  around  it,  or  ]>artly  in  it. 
the  tiny  Solenopsis  galleries  ramifying  through  the  nest  mass 
of  the  host,  and  often  opening  boldly  into  these  large  galleries. 
Througli  their  narrower  }")assages,  too  narrow  to  be  traversed 
by  the  hosts,  the  tiny  thief-ants  thread  their  way  through  the 
host  nest  in  their  burglarious  excursions  (Fig.  245). 

But  there  are  numerous  cases  of  a  less  one-sided  advantage 
in  the  association  of  different  species.  As  an  example  the 
conditions  exhibited  by  the  red-brown  ant.  Mj/rmica  brevi- 
nodes  and  the  smaller  Lcptothorax  emersom  (conditions  made 
known  by  Wheeler's  careful  observations)  may  be  briefly 
described  (Fig.  246).  Thejittle  l.vptothorax  ants  live  in  the 
Myrviica  nests,  building  one  or  more  chambers  with  entrances 
from  the  Myrmica  gall(M'ies,  so  narrow  that  the  large  Myrmi- 
cas  cannot  get  through  them.  When  needing  food  the  Lcpto- 
thorax workers  come  into  the  Myrmica  galleries  and  chambers 
and,  climl)ing  on  the  backs  of  the  Myrmica  workers,  proceed 


376  EVOLUTION   AND   ANIMAL   LIFE 

to  lick  the  face  and  the  back  of  the  head  of  each  host.  A 
Myrmica  thus  treated,  says  Wheeler, 

"paused,  as  if  spellbound  by  this  shampooing  and  occasionally  folded 
its  antennse  as  if  in  sensuous  enjoyment.  The  Leptothorax  after  licking 
the  Myrmica's  pate,  moved  its  head  round  to  the  side  and  began  to 
lick  the  cheeks,  mandibles,  and  labium  of  the  Myrmica.  Such  ardent 
osculation  was  not  bestowed  in  vain,  for  a  minute  drop  of  liquid — 
e\ddently  some  of  the  recently  imbibed  sugar-water — appeared  on  the 
Myrmica' s  lower  lip  and  was  promptly  lapped  up  by  the  Leptothorax. 
The  latter  then  dismounted,  ran  to  another  Myrmica,  climbed  on  its 
back,  and  repeated  the  very  same  performance.  Again  it  took  toll 
and  passed  on  to  still  another  Myrmica.  On  looking  about  in  the  nest 
I  observed  that  nearly  all  the  Leptothorax  workers  were  similarly 
employed." 

Wheeler  believes  that  the  Leptothorax  get  food  only  in  this  way. 
They  feed  their  queen  and  larvae  by  regurgitation.  The 
Myrmicas  seem  not  to  resent  at  all  tlie  presence  of  their  Lepto- 
thorax guests,  and  indeed  may  derive  some  benefit  from  the 
constant  cleansing  licking  of  their  bodies  by  the  shampooers. 
But  the  Leptothorax  workers  are  careful  to  keep  their  queen 
and  young  in  a  separate  chamber,  not  accessible  to  their  hosts. 
This  is  probably  the  part  of  wisdom,  as  the  thoughtless  habit  of 
eating  any  conveniently  accessible  pupse  of  another  species  is 
widespread  among  ants. 

There  are  numerous  interesting  cases  of  symbiosis  in  w^hich 
not  different  kinds  of  animals  are  concerned,  but  animals  and 
plants.  It  has  long  been  known  that  some  sea  anemones 
possess  certain  body  cells  which  contain  chlorophyll,  that  green 
substance  characteristic  of  the  green  plants,  and  only  in  few 
cases  possessed  by  animals.  When  these  chlorophyll-bearing 
sea  anemones  were  first  found,  it  was  believed  that  the  chloro- 
phyll cells  really  belonged  to  the  animal's  body,  and  that  this 
condition  broke  down  one  of  the  chiefest  and  most  readily 
apparent  distinctions  between  animals  and  plants.  But  it 
is  now  known  that  these  chlorophyll-bearing  cells  are  micro- 
scopic, one-celled  plants,  green  algse,  which  live  habitually 
in  the  bodies  of  the  sea  anemone.  It  is  a  case  of  true  symbiosis. 
The  algse,  or  plants,  use  as  food  the  carbon  dioxide  which  is 
given  off  in  the  respiratory  processes  of  the  sea  anemone,,  and 


MUTUAL   AIT)   AXD  COMMUNAL    1.11  i:   AMONG   AXLMALS 


0  4  t 


the  sea  anemone  breathes  \n  tlie  oxygen  given  ofY  \)y  tlie  algio 
in  the  process  of  extracting  the  carlion  for  food  from  the  car- 
bon dioxide.  These  alga*,  or  one-celled  j)lanls,  lie  regularly 
only  in  the  innermost  of  tlie  tliree  cell  layers  whicli  compose 
the  wall  or  body  of  the  sea  anemone  (Fig.  2'M).  They  penetrate 
into  and  lie  in  the  interior  of  the  cells  of  this  layer,  whose  special 
function  is  that  of  digestion.  They  give  this  innermost  layer 
of  cells  a  distinct  green  color.  Even  certain  anKebalikc; 
protozoans  have  been  found  to  contain  individuals  of  a  one- 
celled  alga,  Chlorclla, 
in  their  single-celled 
bodies,  the  tiny  ani- 
mal and  smaller  plants 
living  together  truly 
symbiotically. 

Among  the  higher 
plants  and  animals, 
cases  of  symbiosis  are 
not  rare.  There  lives 
in  the  live-oak  trees 
in  the  vicinity  of  Stan- 
ford University  a  cer- 
tain scale  insect,  Cero- 
coccus  ehrhorni,  which 
differs  from  the  other 
two  or  three  species  of 

its  genus  in  not  having  its  body  covered  b}'  a  heavy,  thick, 
protecting  layer  of  secreted  wax.  Hut  it  gets  the  needed 
protection  in  another  way.  It  is  always  covered  by  a  thick 
feltlike  fungus  growth,  which  lias  ])een  found  by  investiga- 
tion to  germinate  its  spores  and  to  find  a  constant  food 
supply  in  the  "honey  dew"  excreted  by  the  scale  insects. 
This  felt  like  covering  of  fungus,  never  found  to  be  lacking 
in  the  scale  insect,  serves  apparently  as  a  suilicient  sub- 
stitute for  the  heavy,  waxen  mass  conunon  to  the  related 
species. 

The  ants  show  ])articularly  well  instances  of  interesting 
symbiotic  life  with  plants.  Fig.  2o2.  drawn  from  a  specimen 
sent  to  us  from  the  Philippine  Islands  by  the  botanist  Cope- 
land,  shows  some  details  of  one  such  instance.  The  Dis- 
chidias   are   milkweeds   of   the   extreme   Orient.     Tliev  twine 


Fig.  231. — Diagrammatic  section  of  sea  anemone: 
a.  The  inner  cell  layer  contain.s  alga  cclLs,  the 
two  isolated  eelLs  at  the  right  heirig  cells  of  thi.s 
layer  with  contained  alg:r;  6,  midiiie  b<jdy  wall 
layer;  c,  outer  body  wall  layer.    (After  Hertwig.) 


m 


EVOLtJTiON  AND  ANIMAL  LlPE 


upon  trees  by  means  of  their  flexible  St-ems  and  branches  and 
are  especially  noted  for  possessing  appendages  in  the  form  of 
pitchers.  These  pitcherlike  appendages  are  modified  leaves: 
ihe  normal  Dischidia  leaf  is  orbicular,  thick,  and  fleshy.  Each 
pitcher  is  the  blade  of  a  leaf  folded  so  that  the  lower  surface 
forms  the  inner  surface  of  the  pitcher.     Into  these  pitchers 


Fig.  232. — Leaves  of  Dischidia,  which  contain  adventitious  roots  of  the  same  plant 
and  in  which   live  colonies    of   smaU   ants.     (From  specimens   from   Philippine 
■    Islands.) 


grow  adventitious  roots  that  spring  from  the  leaf  peduncle. 
Also  in  these  pitchers  live  colonies  of  ants.  As  rent  for  furnish- 
ing these  comfortable  cozy  little  ant  homes,  the  Dischidia  gets, 
by  means  of  the  adventitious  roots  in  the  pitcher,  food  from 
the  excreta  and  cadavers  of  the  ants.  Hundreds  of  ants  with 
larvae  and  pupae  can  be  found  in  these  Dischidia  leaves,  and 
without  doubt  we  have  here  a  mutually  advantageous  sym- 
biotic adaptation. 

From  Weismann's  chapter  on  Symbiosis  in  his  "Vortrage 
liber  Descendenztheorie,^'  Vol.  I,  1902,  we  translate  the  follow- 


MUTUAL  AID   AND  COMMUNAL   LIFE   AMONG   ANIMALS    379 


ing  account  of  the  s^-mbiosis  of  the  Aztec  ants  and  the  inibauba 
tree: 

"In  the  forests  of  Soutli  America  jijrow  the  inibauba  or  so-called 
candelabra  trees,  species  of  the  genus  Cecropia,  which  well  deserve 
their  name,  'candelabra/  from  the  curious  appearance  given  them 
by  the  outsi)rin<!:ins  bare  branches,  each  Ijeariiip;  a  tuft  of  leaves  at  the 
free  end.  These  leaves  are  often  attacked  by  the  leaf-cutting  ants  of 
the  genus  CEcodonia,  which  roam  by 
tens  of  thousands  over  the  various 
plants  of  the  forest  biting  off  the 
leaves,  that  they  may  fall  to  the  grountl, 
where  they  are  again  seized,  bitten  into 
pieces  and  the  pieces  carried  into  the 
nests  of  the  ants.  In  the  nests  they 
serve  as  a  medium  on  whicli  grow  cer- 
tain molds  or  fun<i;i,  nuich  liked  by  the 
ants.  The  candela])ra  tree  j^rotects  it- 
self from  these  leaf-robbing  enemies  by 
an  association  with  another  ant  species, 
Aztcca  instahilis,  w^hich  finds  safe  dwel- 
ling places  in  the  hollow  trunk  of  the 
tree  and  a  special  supply  of  food  in  a 
brownish  fluid  secreted  by  it.  Along 
the  tree  trunk  occur  in  regular  order 
little  pits  through  which  the  female 
Azteca  can  easily  bore  into  the  interior, 
where  she  lays  her  eggs  and  establishes 
colonies,  so  that  soon  the  interior  of 
the    whole    trunk    swarms    with    ants 

which  rush  out  whenever  the  tree  is  shaken.  But  this  alone  would  not 
serve  to  protect  the  imbauba  from  the  leaf  cutters,  for  how  could  the 
Aztecs  dwellinc;  inside  the  tree  know  of  the  j^resence  of  the  lij;ht-f(K)ted 
leaf -cutters  without?  But  this  is  arranged  for  by  the  devel()j>ment  on 
the  outside  of  the  tree,  at  the  very  points  where  the  thinner  is  greatest, 
namely,  on  the  jietioles  of  the  younp;er  leaves,  of  jKH-uliar  little  hairy 
growths  from  which  j)roject  small  white  «!;rains  which  arc  very  nutri- 
tious and  not  only  easjerly  eaten  by  ants,  but  i^arnercd  by  them  to  carry 
into  their  nests,  jjresumably  as  food  for  their  larva*.  Thus  rij;ht  where 
protection  is  most  needed  the  })l;int  has  develo])ed  a  .^tiwcial  orphan 
attractive  to  the  fierce  Aztec  ants,  so  tiiat  their  constMut  prescncx?  at 


Fig.  233. — Piece  of  a  branch  of 
the  Inibauba  tree,  Cecropia,  the 
leaves  cut  away,  showing  at 
the  base  of  each  petiole  the 
small  tuft  on  the  food;  at  the 
rifiht  some  of  this  ant  food  en- 
largeil.     (After  i;chim;)er.) 


380  EVOLUTION   AND  ANIMAL   LIFE 

these  points  is  an  effective  protection  against  the  encroachments  of 
the  leaf-cutters,  as  courage  and  eagerness  to  fight  other  ants  is  already 
characteristic  of  the  Aztecs.  Not  all  candelabra  trees  live  in  symbiosis 
with  ants  or  possess  this  special  protection  against  the  ravages  of  the 
leaf-cutter  species.  Schimper  found  in  the  forests  of  Brazil  several 
species  of  Cecropia  which  never  shelter  ants  in  the  chambers  of  the 
hollow  trunk.  Now  these  species  do  not  develop  the  curious  special 
food-producing  organs  at  the  bases  of  the  leaf  petioles.  These  species 
lack  the  means  of  attracting  and  retaining  the  ant  guests.  Only  one 
species  of  candelabra  tree,  Cecropia  peltata,  has  develojDed  this  arrange- 
ment, and  it  is  plainly  of  no  direct  use  for  the  tree  except  through  the 
bringing  to  it  of  the  j^rotecting  ants." 

There  are,  of  course,  numerous  other  examples  known  of  the 
symbiotic  association  of  plants  and  animals;  and  if  we  were  to 
follow  the  study  of  symbiosis  into  the  plant  kingdom  we  should 
find  that  in  one  of  the  large  groups  of  plants,  the  familiar 
lichens  which  grow  on  rocks  and  tree  trunks  and  old  fences, 
every  member  lives  symbiotically.  A  lichen  is  not  a  single 
plant,  but  is  always  composed  of  two  plants,  an  alga  (chloro- 
phyll-bearing) and  a  fungus  (without  chlorophyll)  living 
together  in  a  most  intimate,  mutually  advantageous  associa- 
tion. But  we  must  devote  no  more  space  to  the  consideration 
of  this  fascinating  subject. 

The  simplest  form  of  social  life,  or  the  living  together  of 
several  to  many  individuals  of  the  same  sjDecies,  is  shown  among 
those  kinds  of  animals  in  which  many  individuals  of  one  species 
keep  together,  forming  a  great  band  or  herd.  In  this  case  there 
is  not  much  division  of  labor,  and  the  safety  of  the  individual 
is  not  wholly  bound  up  in  the  fate  of  the  herd.  Such  animals 
are  said  to  be  gregarious  in  habit.  The  habit  undoubtedly  is 
advantageous  in  the  mutual  protection  and  aid  afforded  the 
individuals  of  the  band.  This  mutual  help  in  the  case  of 
many  gregarious  animals  is  of  a  very  positive  and  obvious 
character.  In  other  cases  this  gregariousness  is  reduced  to 
a  matter  of  slight  or  temporary  convenience,  possessing  but 
little  of  the  element  of  mutual  aid.  The  great  herds  of  rein- 
deer in  the  north,  and  of  the  bison  or  buffalo  which  once' ranged 
over  the  Western  American  plains,  are  examples  of  a  gregari- 
ousness in  which  mutual  protection  from  enemies,  like  wolves, 
seems  to  be  the  principal  advantage  gained.     The  bands  of 


MUTUAL   AID  AND  COMMUNAL   LIFE   AMUXCi   ANIMALS    3S1 

wolves  which  hunted  the  buffalo  show  the  advimta^'e  of  nuitual 
help  in  aggression  as  well  as  in  protection.  In  this  ])an{hng 
together  of  wolves  there  is  active  cooperation  among  indivichials 
to  obtain  a  common  food  sui)i)ly.  What  one  wolf  cannot  do— 
oliat  is,  tear  down  a  buffalo  from  the  edge  of  the  herd — a  dozen 
can  do,  and  all  arc  gainers  l)y  tlie  operation. 

On  tlie  other  hand,  the  vast  assembhng  of  sea  birds 
on  certain  ocean  islands  and  rocks  is  a  conchtion  i)robal)ly 
brought  about  rather  by  the  si)ecial  suitableness  of  a  few  phices 
for  safe  breeding  than  from  any  sjXM-ial  nuitual  aid  afforded; 
still,  these  sea  birds  und()ul)te(lly  coml)ine  to  drive  off  attack- 
ing eagles  and  hawks.  Eagles  are  usually  considered  to  Ije 
strictly  solitary  in  habit  (the  imit  of  solitariness  being  a  ])air, 
not  an  individual) ;  but  the  description,  by  a  Russian  naturalist, 
of  the  hunting  habits  of  the  great  wliite-tailed  eagle  (Ilali- 
a'etos  alhicilla)  on  the  Russian  stei)i)es  shows  that  this  kind  of 
eagle  at  least  has  adopted  a  gregarious  habit,  in  which  mutual 
help  is  plainly  obvious.  This  naturalist  once  saw  an  eagle 
high  in  the  air,  circhng  slowly  and  widely  in  perfect  silence. 
Suddenlv  the  eagle  screamed  loudlv.  "Its  crv  was  soon  an- 
swered  by  another  eagle,  which  approached  it,  and  was  followed 
by  a  third,  a  fourth,  and  so  on,  till  nine  or  ten  eagles  came  to- 
gether and  soon  disappeared."  The  naturalist,  following  them, 
soon  discovered  them  gathered  about  the  dead  body  of  a  horse. 
The  food  found  by  the  first  was  being  shared  by  all.  The 
association  of  pelicans  in  fishing  is  a  good  examj^le  of  the  ad- 
vantage of  a  gregarious  and  mutually  hel})ful  habit.  The 
peHcans  sometimes  go  fishing  in  great  bands,  and,  after  having 
chosen  an  appropriate  place  near  the  shore,  they  form  a  wide 
half-circle  facing  the  shore,  and  narrow  it  by  j^addling  toward 
the  land,  catching  the  fish  which  they  inclose  in  the  ever- 
narrowing  circle. 

The  wary  Rocky  Mountain  sheep  (Fig.  234)  live  together 
in  small  bands,  posting  sentinels  whenever  they  are  feeding  or 
resting,  who  watch  for  and  give  warning  of  the  a]iproach  of 
enemies.  The  beavers  furnish  a  well-known  and  very  interest- 
ing example  of  mutual  help,  and  they  exhibit  a  truly  com- 
munal life,  although  a  simple  one.  They  live  in  "villages" 
or  communities,  all  hel]Mng  to  build  the  dam  across  the  stream, 
which  is  necessary  to  form  the  broad  marsh  or  pool  in  which  the 
nests  or  houses  are  built.     Prairie  dogs  live  in  great  villages 


382 


EVOLUTION   AND   ANIMAL   LIFE 


Fig.   234. — Rocky  Mountain,   or  bighorn,   sheep.      (By  permission   of   the 

publishers  of  ''  Outing.") 


r-iUTlTAL  AID  AND  COMMUXAL  LIFE   AMONG  ANLMAI.S    3,^.'^ 

./r  communities  wliich  spread  o .  er  many  acres.  Tliey  tell 
t^ach  other  by  shrill  cries  of  the  ai)i)roach  of  enemies,  and  they 
seem  to  visit  eacli  other  and  to  enjoy  each  other's  society  a 
great  deal,  althoiioh  that  they  afford  each  other  nnich  actual 
active  help  is  not  apparent.  Pjirds  in  migration  are  grega- 
rious, although  at  other  times  they  may  live  comparatively 
alone.  In  their  long  flights  they  i^eep  together,  often  with 
definite  leaders  who  seem  to  discover  and  decide  on  tlie  course 


0^ 


^ 


%i. 


-tv 


«»^ 


I     >Tii 


v-^ 


1-iG.  23.j.^rrairic  duKs.      (A<la|)te«l   from  pJiolu- 
graph  \)y  Merriaiii.) 

/       of  flight  for  the  whole  great  flock. 
■i  >  '  The    wedge-shaped    flocks    of    wild 

f  J-  geese  flying  high  and  uttering  their 

sharp,  metallic  call  in  their  south- 
ward migrations  are  well  known  in  many  parts  of  the  Unitetl 
States.  Indeed,  the  more  one  studies  the  habits  of  animals 
the  more  examples  of  social  life  and  mutual  help  will  be  found. 
Probably  most  animals  are  in  some  degree  gregarious  in  habit, 
a.nd  in  all  cases  of  j>Tegariousness  there  is  probabl}-  some  de- 
gree of  mutual  aid. 

An  interesting  series  of  gradations  from  a  strictly  solitary 
through  a  gregarious  to  :t.r.  eial)orately  specialized  comnumal 
life  is  show'n  by  the  bees.  Although  the  buml>lel)ee  and  tlie 
honeybee  are  so  much  move-  familiar  to  us  than  other  bee  kinds 
that  the  communal  life  exemi^lified  bv  them  mav  have  come 

I  ^  k 

to  seem  the  usual  kind  of  l)ee  life,  yet,  as  a  matter  of  fact,  tlierc 
are  many  more  solitary  bees  than  soci;d  ones.  The  general 
character  of  the  domestic  economy  of  the  solitary  bees  is  well 
shown  l)y  the  interesting  little  green  carj)enter  bee.  C'rrafitui 
dupla.  Each  female  of  this  species  bores  out  the  i)itli  fronv 
five  or  six  inches  of  an  eldcM*  branch  or  raspl)erry  cane,  and 


384 


EVOLUTION  AND  ANIMAL  LIFE 


divides  this  space  into  a  few  cells  by  means  of 
transverse  partitions  (Fig.  236).  In  each  cell 
she  lays  an  egg,  and  puts  with  it  enough  food 
— flower  pollen — to  last  the  grub  or  larva 
through  its  hfe.  She  then  waits  in  an  upper 
cell  of  the  nest  until  the  young  bees  issue 
from  their  cells,  when  she  leads  them  off,  and 
each  begins  active  life  on  its  own  account. 
The  mining  bees  Andrena,  which  make  little 
burrows  (Fig.  237)  in  a  clay  bank,  live  in  large 
colonies — that  is,  they  make  their  nest  bur- 
rows close  together  in  the  same  clay  bank,  but 
each  female  makes  her  own  burrow,  lays  her 
own  eggs  in  it,  furnishes  it  with  food — a  kind 
of  paste  of  nectar  and  pollen — and  takes  no 
further  care  of  her  young.  Nor  has  she  at  any 
time   any  special  in- 


Fig.  236.— Nest 
of  carpenter 
bee,  Ceratina 
dupla. 


terest  in  her  neigh- 
bors. But  with  the 
smaller  mining  bees, 
belonging  to  the 
genus  Halictus,  several 
females  unite  in  mak- 
ing a  common  burrow,  after  which 
each  female  makes  side  passages  of 
her  own,  extending  from  the  main  or 
public  entrance  burrow.  As  a  well- 
known  entomologist  has  ssiid,  Andrena 
builds  villages  composed  of  individual 
homes,  while  Halictus  makes  cities 
composed  of  apartment  houses.  The 
bumblebee  (Fig.  238),  however,  es- 
tablishes a  real  community  with  a 
truly  communal  life,  although  a  very 
simple  one.  The  few  bumblebees 
which  we  see  in  winter  time  are 
queens;  all  other  bumblebees  die  in 
the  autumn.  In  the  spring  a  queen 
selects  some  deserted  nest  of  a  field 
mouse,  or  a  hole  in  .the  ground, 
gathers  pollen  which  she  molds  into 


Fig,  237. — Nest  of  the  Andrena, 
the  mining  bee. 


MUTUAL   AID   AND  COMMUNAL   LIFE   AMONG    ANLMALS    385 


a  rather  large  irregular  mass  and  puts 

into  the  hole,  and  lays  a  few  eggs  on 

the  pollen  mass.     Tlio  young  grubs  or 

larvse   whicli    soon    hatch    feed    on    the 

pollen,    grow,     pupate,    and     issue    as 

workers — winged    bees    a    little    smaller 

than  the   queen.     These  workers   luring 

more  pollen,  enlarge  the  nest,  and  make 

irregular  cells  in  the  j^ollen  mass,  in  each 

of   which  the  queen  la3's   an  egg.     She 

gathers  no  more   pollen,  does  no  mo'*e 

work  except  that  of  egg-laying.     From 

these    new"    eggs    are     })roduced    more 

workers,  and    so    on    until    tlie    com- 

munity  may  come   to   be   pretty  large. 

Later  in  the  summer  males  and  females 

are  produced  and  mate.     With  the  ap- 
proach of   winter   all   tlie   worko;s   and 

males    die,    leaving    only    the    ferlihzcd 

females,    the    queens,    to    live    through 

the  winter  and  found  new  communities 

in  the  spring. 

The  social  wasps — as  with  tlie  bees, 

there  are  many  more  kinds 
of  solitary  wasps  than  social 
ones — show  a  connnunal  life 
like  that  of  the  bumblebees. 
The  onlv  vellow  jackets  and 
hornets  that  live  through 
the  winter  are  fertilizi'd 
females  or  queens.  \\'hen 
spring  comes  each  ciuet'ii 
builds  a  small  nest  sus- 
pended from  a  tree  branch, 
or  in  a  hole  in  the  ground. 
wliich  consists  of  a  small 
comb  inclosed  in  a  ct)vei  ing 
or  env(>l()pe  open  at  the 
lower  end.  The  nest  is 
composed  of  "wasp  paper," 


Fig.  238.— BumMebeos:  a. 
Worker;  b,  queen  or  fer- 
tile female. 


^^ 


Fl<J'  239— The  yellow  jacket,  Vespa.  a  social 
Wftiip"    a.  Worker;  b,  queen. 


made   by  clicking  !.)its   of 


386 


EVOLUTION  AND  ANIMAL  LIFE 


weather-beaten  wood  taken  from  old  fences  or  outbuildings. 
In  each  of  the  cells  the  queen  lays  an  egg.  She  deposits  in  the 
cell  a  small  mass  of  food,  consisting  of  some  chewed  insects 
or  spiders.  From  these  eggs  hatch  grubs  which  eat  the  food 
prepared  for  them,  grow,  pupate,  and  issue  as  worker  wasps. 


^i 


Fig,  240. — At  the  left,  nest  of  Verpa,  a  social  wasp;  at  the  right,  nest  of  Vespa  opened 

to  show  combs  within.     (From  photographs.) 


winged  and  slightly  smaller  than  the  queen  (Fig.  239).  The 
workers  enlarge  the  nest,  adding  more  combs  and  making 
many  cells,  in  each  of  which  the  queen  lays  an  egg.  The 
workers  provision  the  cell  with  chewed  insects,  and  other  broods 
of  workers  are  rapidly  hatched.  The  community  grows  in  num- 
bers and  the  nest  grows  in  size  until  it  comes  to  be  the  great 
ball-like  oval  mass  which  we  know  so  well  as  a  hornets'  nest 
(Fig-.  240),  a  thing  to  be  left  untouched.  When  disturbed, 
the  wasps  swarm  out  of  the  nest  and  fiercely  attack  any 
invading  foe  in  sight.  After  a  number  of  broods  of  workers 
has  been  produced,  broods  of  males  and  females  appear  and 
mating  takes  place.  In  the  late  fall  the  males  and  all  of  the 
many  workers  die,  leaving  only  the  new  queens  to  live  through 
the  winter. 

Honeybees  live  together,  as  we  know,  in  large  communities. 


Mutual  aid  and  communal  life  among  animals  :^9>7 


We  are  accustomed  to  think  of  lioncyl^ees  as  the  inhabuam* 
of  beehives,  but  there  were  bees  before  there  were  hives.  The 
"bee  tree"  is  famihar  to  many  of  us.  Tiie  bees,  in  Nature, 
make  their  home  in  the  liollow  of  some  dead  or  decaying  tree- 
trunk,  and  carry  on  there  all  the  industries  which  characterize 
the  busy  communities  in  the  liives.  A  honeyl)ee  communitv 
comprises  three  kinds  of  individuals  (Fig.  241) — namely,  a 
fertile  female  or  queen,  numerous  males  or  drones,  and  many 
infertile  females  or  workers.  These  three  kinds  of  individuals 
differ  in  external  appearance  sufficiently  to  be  reathly  recogniz- 
able. The  workers  are  smaller  tlian  the  (pieens  and  drones, 
and  the  last  two  differ  in  the  shape  of  the  abdomen,  or  hind 
body,  the  abdomen  of  the  queen  lacing  longer  and  more  slender 
than  that  of  the  male  or  drone.  In  a  single  conununity  there 
is  one  queen,  a  few  hundred  drones,  and  ten  to  thirty  thousand 
workers.  The  number  of  drones  and  workers  varies  at  different 
limes  of  the  year,  being  smallest  in  winter.  Each  kind  of 
individual  has  certain  work  or  business  to  do  for  the  wliole 
community.  The  cpieen  lays  all  the  eggs  from  which  new  bees 
are  born;  that  is,  she  is  the  mother  of  the  entire  conununity. 
The  drones  or  males  have  simply  to  act  as  royal  consorts;  u})()n 
them  depends  the  fertilization  of  the  eggs.  The  workers 
undertake  all  the  food-getting,  the  care  of  the  young  bees,  the 


Fig.  241.— fHoneybee:  a,  Drone  or  male;  6,  worker  or  female;  r,  queen  «)r  fertile  female. 

comb-building,  the  honey-making — all  the  industries  with  which 
we  are  more  or  less  familiar  that  are  carried  on  in  the  hive. 
And  all  the  work  done  by  the  workers  is  strictly  work  for  the 
whole  community;  in  no  case  does  tlie  worker  bee*  work  for 
itself  alone;  it  works  for  itself  only  in  so  far  as  it  is  a  member  of 

the  community. 

How  varied  and  (>laborately  jn-rfected  th(\se  industries  are 
may  be  perceived  from  a  brief  account  of  the  life  history  of  a 


38S 


EVOLUTION  AND  ANIMAL  LIFE 


bee  community.  The  interior  of  the  hollow  in  the  bee  tree  oi* 
of  the  hive  is  filled  with  "comb" — that  is,  with  wax  molded 
into  hexagonal  cells  and  supports  for  these  cells.     The  molding 

of  these  thousands  of  symmetrical  cells  is 
accomplished  by  the  w^orkers  by  means  of 
their  specially  modified  trowellike  mandibles 
or  jaws.  The  wax  itself,  of  which  the  cells 
are  made,  comes  from  the  bodies  of  the 
workers  in  the  form  of  small  liquid  drops 
which  exude  from  the  skin  on  the  under 
side  of  the  abdomen  or  hinder  body  rings. 
These  droplets  run  together,  harden  rrd 
become  flattened,  and  are  removed  f:om 
the  Vv^ax  plates,  as  the  peculiarly  modified 
parts  of  the  skin  which  produce  the  wax 
are  called,  by  means  of  the  hind  legs,  which 
are  furnished  with  scissorlike  contrivances 
for  cutting  off  the  Avax  (Fig.  242).  In  cer- 
tain of  the  cells  are  stored  the  pollen  and 
honey,  which  serve  as  food  for  the  com- 
munity. The  pollen  is  gathered  by  the 
workers  from  certain  favorite  flowers  and  is 
carried  bv  them  from  the  flowers  to  the 
hive  in  the  "pollen  baskets,"  the  slightly 
concave  outer  surfaces  of  one  of  the  seg- 
ments of  the  broadened  and  flattened  hind 
legs.  This  concave  surface  is  lined  on  each 
margin  with  a  row  of  incurved  stiff  hairs, 
which  hold  the  pollen  mass  securely  in  place 
(Fig.  242).  The  "honey"  is  the  nectar  of 
flowers  which  has  been  sucked  up  by  the 
workers  by  means  of  their  elaborate  lapping 
and  sucking  mouth  parts  and  swallowed 
into  a  sort  of  honey  sac  or  stomach,  then 
brought  to  the  hive  and  regurgitated  into 
the  cells.  This  nectar  is  at  first  too  watery 
to  be  good  honey,  so  the  bees  have  to  evaporate  some  of  this 
water.  Many  of  the  workers  gather  above  the  cells  contain- 
ing nectar,  and  buzz — that  is,  vibrate  their  wings  violently. 
This  creates  currents  of  air  which  pass  over  the  exposed  nectar 
and  increase  the  evaporation  of  the  water.     The  violent  buzz- 


Fig.  242. — Posterior 
leg  of  worker  honey- 
bee. Concave  sur- 
face of  the  upper 
large  joint  with  the 
marginal  hairs  is 
the  pollen  basket; 
the  wax  shears  are 
the  cutting  surfaces 
of  the  angle  be- 
tween the  two  large 
segments  of  the  leg. 


MUTUAL  AID   AND  COMMUNAL   LIFE   AMOXG   ANBLVLS    3R^ 


ing  raises  the  temperature  of  tlie  ])ces'  l)odies,  and  this  warmth 
given  off  to  the  air,  also  lielps  make  evaporation  more  rapid. 
In  addition  to  bringing  in  food  tlie  workers  also  bring  in,  when 
necessary,  "propolis,"  or  the  resinous  guni  of  certain  trees, 
which  they  use  in  repairing  the  hive,  as  closing  uj)  cracks  and 
crevices  in  it. 

In  many  of  the  cells  there  will  be  found,  not  jiollen  or 
honey,  but  the  eggs  or  the  young  bees  in  larval  or  pupal  con- 
dition (Fig.  243).  The  cpieen  moves  about  through  the  hive, 
hiying  eggs.  She  deposits  only  one  egg  in  a  cell.  In  three 
days  the  egg  liatches, 
and  the  yoimg  l^ee  ap- 
pears as  a  heli)less  soft, 
white,  footless  gi-ul)  or 
larva.  It  is  cared  for 
by  certain  of  the 
workers,  that  mav  be 
called  nurses.  These 
nurses  do  not  differ 
structurally  from  the 
other  workers,  but  they 
have  the  sjoecial  duty 
of  caring  for  the  help- 
less young  bees.  They 
do  not  go  out  for  pol- 
len or  honey,  but  stay  in  the  hive.  They  are  usually  the 
new  bees — i.  e.,  the  youngest  or  most  recently  added  workers. 
After  they  act  as  nurses  for  a  week  or  so  they  take  their 
places  with  the  food-gathering  workers,  and  other  new  })ees 
act  as  nurses.  The  nurses  feed  the  yoimg  or  larval  bees  at 
first  with  a  highly  nutritious  food  called  bee  jelly,  whicli  the 
nurses  make  in  their  stomach,  and  regm-gitate  for  the  larva\ 
After  the  larvae  are  two  or  three  days  old  they  are  fed  with  jjollrn 
and  honey.  Finally,  a  small  mass  of  food  is  ]Mit  into  the  cell, 
and  the  cell  is  "capped  "or  covered  with  wax.  I^ach  larva, 
after  eating  all  its  food,  in  two  or  three  days  more  changes  into 
a  pupa,  which  lies  cpiiescent  without  eating  for  thirteen  days, 
when  it  changes  into  a  full-grown  l)ee.  The  new  l)ee  breaks 
open  the  cap  of  the  cell  with  its  jaws,  and  comes  out  into  the 
hive,  ready  to  take  up  its  share  of  tlie  work  for  tlie  conununity. 
In  a  few  cases,  however,  the  lif(>  history  is  dilTcn^it .  Tlie  nursed 
26 


Fig.  243. — Cells  containing  eggs,  larvrr,  and  pupa? 
of  the  honeybee.  The  lower,  large,  irregular  cells 
are  the  queen  cells.      (After  Benton.) 


390  EVOLUTION  AND  ANIMAL  LIFE 

will  tear  down  several  cells  around  some  single  one,  and  enlarge 
this  inner  one  into  a  great  irregular  vase-shaped  cell.  When 
the  egg  hatches,  the  grub  or  larva  is  fed  bee  jelly  as  long  as  it 
remains  a  larva,  never  being  given  ordinary  pollen  and  honey 
at  all.  This  larva  finally  pupates,  and  there  issues  from  the 
pupa  not  a  worker  or  drone  bee,  but  a  new  queen  bee.  The  egg 
from  which  the  queen  is  produced  is  the  same  as  the  other  eggs, 
but  the  worker  nurses  by  feeding  the  larva  only  the  highly 
nutritious  bee  jelly  make  it  certain  that  the  new  bee  shall  be- 
come a  queen  instead  of  a  w^orker.  It  is  also  to  be  noted  that 
the  male  bees  or  drones  are  hatched  from  eggs  that  are  not 
fertilized,  the  queen  having  it  in  her  power  to  lay  either  ferti- 
lized or  unfertilized  eggs.  From  the  fertilized  eggs  hatch 
larvse  which  develop  into  queens  or  workers,- depending  on 
the  manner  of  their  nourishment;  from  the  unfertilized  eggs 
hatch  the  males.. 

When  several  queens  appear  there  is  much  excitement 
in  the  community.  Each  community  has  normally  a  single 
one,  so  that  when  additional  queens  appear  some  rearrange- 
ment is  necessary.  This  rearrangement  comes  about  first  by 
fighting  among  the  queens  until  only  one  of  the  new  queens  is 
left  alive.  Then  the  old  or  mother  queen  issues  from  the  hive 
or  tree  follow^ed  by  many  of  the  workers.  She  and  her  followers 
fly  away  together,  finally  alighting  on  some  tree  branch  and 
massing  there  in  a  dense  swarm.  This  is  the  familiar  phenome- 
non of  "swarming."  The  swarm  finally  finds  a  new  hollow 
tree,  or  in  the  case  of  the  hive  bee  the  swarm  is  put  into  a 
new  hive,  where  the  bees  build  cells,  gather  food,  produce 
young,  and  thus  found  a  new  community.  This  swarmmg 
is  simply  an  emigration,  which  results  in  the  wider  distribu- 
tion and  in  the  increase  of  the  number  of  the  species.  It  is  a 
peculiar  but  effective  mode  of  distributing  and  perpetuating 
the  species. 

There  are  many  other  interesting  and  suggestive  things 
which  might  be  told  of  the  life  in  a  bee  community:  how  the 
community  protects  itself  from  the  dangers  of  starvation 
when  food  is  scarce  or  winter  comes  on  by  killing  the  useless 
drones  and  the  immature  bees  in  egg  and  larval  stage;  how 
the  instinct  of  home-finding  has  been  so  highly  developed 
that  the  worker  bees  go  miles  aw^ay  for  honey  and  nectar, 
flying  with  unerring  acciu-acy  back  to  the  hive;  of  the  extraor- 


MUTUAL  AID  AMD  COMMUNAL   LIFE   AMONG   AXLMAI^    391 

dinarily  nice  structural  modifications  which  adapt  tlie  l^ec  so 
perfectly  for  its  com})lex  and  varied  businesses;  and  of  tlie 
tireless  persistence  of  the  workers  until  they  fall  exhausted 
and  dying  in  the  performance  of  their  duties.  Tlic  connnunity, 
it  is  important  to  note,  is  a  persistent  or  continuous  one.  The 
workers  do  not  live  long,  the  s})ring  broods  usually  not  over 
two  or  three  months,  and  tlie  fall  broods  not  more  tlian  six  or 
eight  months;  but  new  ones  are  hatching  while  the  old  ones  arc 
I'ying,  and  the  community  as  a  whole  always  persists.     The 


Fig.  244. — Female  (a),  male  (6)    and  worker  (c)  of  an  ant,  Camponotua  sp. 


queen  may  live  several  years,  perhaps  as  many  as  five.'     She 
lays  about  one  million  eggs  a  year. 

There  are  many  species  of  ants,  two  tliousand  or  more,  and 
all  of  them  live  in  communities  and  show  a  truly  coinininial 
life.  There  is  much  variety  of  ha])it  in  the  lives  of  different 
kinds  of  ants,  and  the  degree  in  which  the  communal  or  social 
life  is  specialized  or  elaborated  varies  much.  Jkit  certain 
general  conditions  })revail  in  the  life  of  all  tlie  different  kinds  of 
individuals — sexually  develojunl  males  and  females  that  pos.«;es8 
wings,  and  sexually  undeveloped  workers  that  are  winglcsa 
(Fig.  244).  In  some  kinds  the  workers  show  structural  difTer- 
ences  among  themselves,  being  divided  into  small  workers, 
large  workers,  and  soldiers.     The  workers  are,  as   with   the 


<j '  -T  ■ 


.  ^  A  queen  bee  has  bft-n  kept  alive  for  fifteen  years. 


392 


EVOLUTION   AND   ANIMAL   LIFE 


bees,  infertile  females.  Although  the  life  of  the  ant  communities 
is  much  lesG  familiar  and  fully  known  than  that  of  the  bees,  it 
is  even  more  remarkable  in  its  specializations  and  elaborate- 
ness. The  ant  home,  or  nest,  or  formicary,  is,  with  most 
species,  a  very  elaborate  under gi^ound,  many-storied  labyrinth 
of  galleries  and  chambers.     Certain  rooms  are  used  for  the 

storage  of  food ;  certain 

h        c 


"nurseries'^ 


others   as 

for  the  reception  and 
care  of  the  young;  and 
others  as  '^stables  "  for 
the  ants'  cattle,  certain 
plant  lice  or  scale  in- 
sects which  are  some- 
times collected  and 
cared  for  by  the  ants. 

The  food  of  ants 
comprises  many  kinds 
of  vegetable  and  ani- 
mal substances ;  but 
the  favorite  food,  or 
"national  dish,"  as  it 
has  been  called,  is  a 
sweet  fluid  which  is 
produced  by  certain 
small  insects,  the  plant 
lice  (Aphididse)  and 
scale  insects  (Coccidae). 
These  insects  live  on 
the  sap  of  plants;  rose  bushes  are  especially  favored  with  their 
presence.  The  worker  ants  (and  we  rarely  see  any  ants  but  the 
wingless  workers,  the  winged  males  and  females  appearing  out  of 
the  nest  only  at  mating  time)  find  these  honey-secreting  insects, 
and  gently  touch  or  stroke  theni  w^ith  their  feelers  (antennae) , 
when  the  plant  lice  allow  tiny  drops  of  the  honey  to  issue  from 
the  body,  which  are  eagerly  drunk  by  the  ants.  It  is  manifestly 
to  the  advantage  of  the  ants  that  the  plant  lice  should  thrive ;  but 
they  are  soft-bodied,  defenseless  insects,  and  readily  fall  a  prey 
to  the  wandering  predaceous  insects  like  the  ladybirds  and 
aphis  lions.  So  the  ants  often  guard  small  groups  of  plant 
lice,  attacking,  and  driving  away  the  would-be  ravagers.     When 


IG.  245. — ^The  ant,  Solenopsis  fugax:  a,  Male;  b, 
dealated  female;  c,  worker;  d,  portion  of  nest  show- 
ing broad  galleries  of  the  host  ant  intersected  by 
the  tenuous  galleries  of  Solenopsis,  the  thief  ant. 
(After  Wasmann.    See  account  on  page  375.) 


MUTUAL   AID  AND  COMMUXAL   LIFE   AMONG   ANIMALS    393 


y 


the  branch  on  wliicli  tlie  j)hinl  hcc  jirc  ^ets  withomi  and  dry 
the  ants  liave  been  obser\'ecl  to  carry  the  phmt  Hce  earcfiiliy 
to  a  fresh,  green  brancli.  On  page  374  is  deserilx'd  liow  the 
httle  brown  ant  Lasius  brunneus  cares  for  the  corn  root  plant 
louse.  In  the  arid  kinds  of  New  Mexico  and  Arizona  the  ants 
rear  theh*  scale  insects  on  the  roots  of  cactus.  Other  kinds  of 
ants  carry  plant  lice  into  their  nests  and  provide  them  with  frxxl 
there.  Because  the  ants  ol)- 
tain  food  from  the  i)lant  lice 
and  take  care  of  them,  the 
plant  lice  are  not  inaptly 
called  the  ants'  cattle. 

Like  the  honeybees,  the 
young  ants  are  helpless 
httle  grubs  or  larvae,  and 
are  cared  for  and  fed  by 
nurses.  The  so-called  ants' 
eggs,  little  white,  oval 
masses,  which  we  often 
see  being  carried  in  the 
mouths  of  ants  in  and  out 
of  ants'  nests,  are  not  eggs, 
but  are  the  pupae  which 
are  being  brought  out  to 
enjoy  the  warmth  and  light 
of  the  sun  or  being  taken 
back  into  the  nest  after- 
wards. 

In  addition  to  the  w^orkers  that  build  the  nest  and  collect 
food  and  care  for  the  plant  lice,  there  is  in  many  species  of 
ants  a  kind  of  individuals  called  soldiers.  These  are  wingless, 
like  the  workers,  and  are  also,  like  the  workers,  not  capal)le  of 
laying  or  of  fertilizing  eggs.  It  is  the  business  of  the  soldiers, 
as  their  name  suggests,  to  fight.  They  protect  the  community 
by  attacking  and  driving  away  ])redaceous  insects,  especially 
other  ants.  The  ants  are  among  the  most  warlike  of  in.sects. 
The  soldiers  of  a  comnnmity  of  one  species  of  ant  often  sally 
forth  and  attack  a  comnnmity  of  some  other  speci(\s.  If  suc- 
cessful in  battle  the  workers  of  the  victorious  conununity  take 
possession  of  the  food  stores  of  tlie  con<|uer(Ml  ami  carry  them 
to  their  own  nest.     Indeed,  they  go  even  further;  they  may 


Fig.  246. — Nest  of  the  ant,  Leptothorax  emer- 
soni,  with  the  nest  of  another  ant.  .\fi/rmica 
scahr'nuxtes.  (See  account  on  piMje  375.) 
(After  Wheeler.) 


394  EVOLUTION  AND  ANIMAL  LIFE 

make  slavea  of  the  conquered  rnts.  '  There  are  numerous 
species  of  th^  so-called  slave-making  ants.  The  slave-makers 
carry- into  their  own  nest  the  eggs  and  larvae  and  pupae  of  the 
conquered  community,  and  when  these  come  to  maturity  they 
act  as  slaves  of  the  victors — that  is,  they  collect  food,  build 
additions  to  the  nests,  and  care  for  the  young  of  the  sla^ve- 
makers.  This  specialization  goes  so  far  in  the  case  of  some 
kinds  of  ants,  like  the  robber-ant  of  South  America  {Ecitoa), 
that  all  of  the  Eciton  w^orkers  have  become  soldiers,  which  no 
longer  do  any  work  for  themselves.  The  whole  community 
lives,  therefore,  wholly  by  pillage  or  by  making  slaves  of  other 
kinds  of  ants.  There  are  four  kinds  of  individuals  in  a  robber- 
ant  community — winged  males,  winged  females,  and  small  and 
large  wingless  soldiers.  There  are  many  more  of  the  small 
soldiers  than  of  the  large,  and  some  naturalists  believe  that  the 
few  latter,  which  are  distinguished  by  heads  and  jaws  of  great 
size,  act  as  ofhcei^s!  On  the  march  the  small  soldiers  are  ar- 
ranged in  a  long,  na,rrow  column,  while  the  large  soldieis  are 
scattered  along  on  either  side  of  the  column  and  appear  to  act 
as  sentinels  and  directors  of  the  army.  The  observations  made 
by  the  European  students  of  ants,  Huber.  Foiel,  Emery  and 
VVasmann,  and  by  McCook  and  Wheeler  in  America,  read  like 
fairy  tales,  and  yet  are  the  well-attested  actual  phenomena  of 
the  extremely  specialized  communal  and  social  life  of  these 
animals. 

The  bumblebees  and  social  wasps  show  an  intermediate 
condition  between  the  simply  gregarious  or  neighborly  mining 
bees  and  the  highly  developed,  permanent  honeybee  and  ant 
communities.  Natm^alists  believe  that  the  highly  organized 
communal  life  of  the  honeybees  and  the  ants  is  a  develop- 
ment from  some  simple  condition  like  that  of  the  bumblebees 
and  social  wasps,  which  in  its  turn  has  grown  out  of  a  still 
simpler,  more  gregarious  assembly  of  the  individuals  of  one 
species.  It  is  not  difficult  to  see  how  such  a  development  could 
in  the  course  of  a  long  time  take  place.  \ 

The  termites  or  white  ants  (not  true  ants)  are  also  communal 
insects.  Some  species  of  termites  in  Africa  live  in  great  mounds 
of  earth,  often  fifteen  feet  high.  The  community  comprises 
hundreds  of  thousands  of  individuals,  which  are  of  as  many  as 
eight  kinds  or  castes  (Fig.  247)  viz.,  sexually  active  winged  males, 
sexually  active  winged  females,  other  fertile  males  and  females 


MUTUAL   AID   AND  COMMUNAL   LIFE   .\.\lONG   ANLMALS    395 


which  are  wingless,  wingless  workers  of  both  sexes  not  capaljle 
of  reproduction,  and  wingless  soldiers  of  both  sexes  also  in- 
capable of  reproduction.  The  production  of  new  in(hvi(hials 
is  the  sole  business  of  the  fertile  males  and  females;  the  workers 
build  the  nest  and  collect  food,  and  the  soldiers  i)rotect  the 
connuunity  from  the  attacks  of  marauding  insects.  The  egg- 
laying  queen  grows  to  monstrous  size  in  some  species,  being  some- 
times four  or  five  inches  long,  while  the  other  individuals  of  the 
community  are  not 
more  than  half  or 
three-quarters  of  an 
inch  long.  The  great 
size  of  the  queen  is 
due  to  the  enormous 
number  of  eggs  in 
her  body. 

We  have  pointed 
out  elsewhere  that 
the  complexity  of 
the  bodies  of  the 
higher  animals  de- 
pends on  a  specirli- 
zation  or  different ir.- 
tion  of  parts,  due 
to  the  assumption  of 
different  functions  or 
duties    by    different 

parts  of  the  body;  that  the  degree  of  structural  differentiation 
depends  on  the  degree  or  extent  of  division  of  labor  shown  in 
the  economy  of  the  animr.l.  It  is  obvious  that  the  same  jirin- 
ciple  of  division  of  \v.hor  with  accomi)anying  modihcation  of 
structure  is  the  basis  of  colonial  and  conununal  life.  It  is 
simply  a  manifestation  of  the  princii)le  among  individuals  in- 
stead"^of  among  organs.  Tlie  division  of  the  necessary  labois 
of  life  among  the  different  zooids  of  the  colonial  jellyfisli  is 
plainlv  the  reason  for  the  profound  and  striking.- but  always 
reasonable  and  ex])lical)le,  modihcations  of  the  typical  iH>lyp 
or  medusa  IkkIv,  wliich  is  shown  by  the  swinuning  zooids,  the 
feeding  zooids,  the  sense  zooids,  and  the  others  of  the  colony. 
And  similarlv  in  the  case  of  the  termite  community,  the  sol- 
dier individuals  are  difTerent  structurally  from  the  worker  i-- 


FiG.  247. — Termites:    a,  Queen;    b,  male;  c,  worker; 

d.  soltliiT. 


396  EVOLUTION   AND   ANIMAL   LIFE 

clividuals  because  of  the  different  work  they  have  to  do.  And 
the  queen  differs  from  all  the  others,  because  of  the  extraor- 
dinary proUficacy  demanded  of  her  to  maintain  the  great  com- 
munity. 

It  is  important  to  note,  however,  that  among  those  animals 
that  show  the  most  highly  organized  or  specialized  communal 
or  social  life,  the  structural  differences  among  the  individuals 
are  the  least  marked,  or  at  least  are  not  the  most  profound. 
The  three  kinds  of  honeybee  individuals  differ  but  little;  in- 
deed, as  two  of  the  kinds,  mcAe  and  female,  are  to  be  found  in 
the  case  of  almost  all  kinds  of  animals,  wliether  communal 
in  habit  or  not,  the  only  unusual  structural  si3ecialization  in 
the  case  of  the  honeybee,  is  the  presence  of  the  worker  indi- 
vidual, which  differs  from  the  other  individuals  primarily  in 
the  rudimentary  condition  of  the  reproductive  glands.  Finally, 
in  the  case  of  man,  with  whom  the  communal  or  social  habit 
is  so  all-important  as  to  gain  for  him  the  name  of  "the  social 
animal, ^^  there  is  no  differentiation  of  individuals  adapted 
only  for  certain  kinds  of  work.  Among  these  highest  ex- 
amples of  social  animals,  the  presence  of  an  advanced  mental 
endowment,  the  specialization  of  the  mental  power,  the  power 
of  reason,  have  taken  the  place  of  and  made  unnecessary  the 
structural  differentiation  of  individuals.  The  honeybee  work- 
ers do  different  kinds  of  work:  some  gather  food,  some  care  for 
the  young,  and  some  make  wax  and  build  cells,  but  the  in- 
dividuals are  interchangeable;  each  one  knows  enough  to  do 
these  various  things.  There  is  a  structural  differentiation  in 
the  matter  of  only  one  special  work  or  function,  that  of  re- 
production. 

With  the  ants  there  is,  in  some  cases,  a  considerable  struc- 
tural divergence  among  individuals,  as  in  the  genus  Atta  of 
South  America  with  six  kinds  of  individuals — namely,  winged 
males,  winged  females,  wingless  soldiers,  and  wingless  workers 
of  three  distinct  sizes.  In  the  case  of  other  kinds  with  cjuite 
as  highly  organized  a  communal  life,  there  .are  but  three  kinds 
of  individuals;  the  winged  males  and  females  and  the  wingless 
workers.  The  workers  gather  food,  build  the  nest,  guard  the 
"cattle"  (aphids),  make  war,  and  care  for  the  A^oung.  Each 
one  knows  enough  to  do  all  these  various  distinct  things.  Its 
body  is  not  so  modified  that  it  is  limited  to  doing  but  one 
kind  of  thing. 


MUTUAL   AID   AND   COMMUNAL   LIFE   AMONG   ANLMAL6    3U7 

The  increr.se  of  intelligence,  the  development  of  the  ix)wer 
of  reasoning,  is  tl:e  most  potent  factor  in  the  development  of 
a  highly  specialized  social  lif3,  Man  is  the  example  of  the 
hi^jhest  development  of  this  sort  in  the  animal  kingilom,  hut 
the  highest  form  of  social  development  is  not  by  any  means  the 
most  perfectly  communal. 

The  advantages  of  communal  or  social  life,  of  cooperation 
and  mutual  aid,  are  real.  The  animals  that  have  a{l{)|)ted 
such  a  life  are  among  the  most  successful  of  all  animals  in  th(i 
struggle  for  existence.  The  termite  individual  is  one  of  the 
most  defenseless,  and,  for  those  animrJs  thrt  prey  on  insects, 
one  of  the  most  toothsome  luxuries  to  be  found  in  the  insect 
world.  But  the  termite  is  one  of  the  most  abundant  and 
widespread  and  successfully  living  insect  kinds  in  all  the  tropics. 
Where  ants  are  not,  few  insects  are.  The  honeybee  is  a  popu- 
lar type  of  a  successful  life.  The  artificial  protection  afTordcd 
the  honeybee  by  man  may  aid  in  its  struggle  for  existence,  Init 
it  gains  this  protection  because  of  certain  features  of  its  com- 
munal life,  and  in  Nature  the  honey l)ee  takes  care  of  itself 
well.  The  Little  Bee  People  of  Kii)ling's  Jungle  J^ook,  who 
live  in  great  communities  in  the  rocks  of  Indian  hills,  can  put  to 
rout  the  largest  and  fiercest  of  the  jimgle  animals.  Coopera- 
tion and  mutual  aid  are  among  the  most  important  factors 
which  help  in  the  struggle  for  existence.  Its  great  advantages 
are,  however,  in  some  degree  balanced  by  the  fact  that  mutual 
help  brings  mutual  dependence.  Tlie  comnnmity  or  society 
can  accomplish  greater  things  than  the  solitary  individuals, 
but  codperation  limits  freedom,  and  often  sacrifices  the  indi- 
vidual to  the  whole. 


CHAPTER  XIX 
COLOR  AND   PATTERN   IN  ANIMALS 

In  spite  of  the  fluency  with  which  so  many  people  talk  of  the 
meaning  of  color  in  organisms,  the  subject  is  as  incomplete  on  the 
theoretical  as  on  the  physiological  side.  .  .  .  The  two  deficiencies  are 
related  and  a  little  more  j^hysiology  will  arm  the  theorists  with  better 
weapons. — Newbigin. 

A  CONSPICUOUS  characteristic  of  the  animal  body  is  its  color 
pattern.  Not  all  kinds  of  animals  attract  our  attention  by 
their  colors :  there  are  even  whole  groups  whose  uniform  mono- 
chrome color  scheme  is  of  a  sort  to  relieve  them  completely 
from  any  imputation  of  flaunting  showiness  or  of  bizarre  fancies 
in  personal  decoration.  But  consider  such  a  class  as  the  insects : 
the  painted  butterflies,  the  burnished  beetles,  the  flashing 
dragon  flies,  the  green  katydids  and  brown  locusts  All  attract 
attention  first  by  the  variety  or  intensity  of  their  colors  and 
the  arrangement  of  these  colors  in  simple  or  intricate  symmetry 
of  pattern.  Even  the  small  and  at  casual  glance,  obscure  and 
monochrome  insects  often  reveal,  on  careful  examination,"  a 
large  degree  of  color  development  and  ofttimes  amazing  in- 
tricac}^  and  beauty  of  pattern.  So  uniformly  developed  is 
color  pattern  among  insects,  that  no  thoughtful  collector  or 
observer  of  these  animals  escapes  the  self-put  question:  Why 
is  there  such  a  high  degree  of  specialization  of  color  throughout 
the  insect  class?  If  he  be  an  observer  w^ho  has  taken  seriouslv 
the  teachings  of  Darwin  and  the  utilitarian  school  of  naturalists, 
his  question  becomes  couched  in  this  form:  What  is  the  use  to 
the  insects  of  all  this  color  and  pattern? 

For  the  attitude  of  any  modern  student  of  Nature,  con- 
fronted by  such  a  phenomenon,  is  that  of  the  seeker  for  the 
significance  of  the  phenomenon.     And  the  key  to  significance 

m 


COLOR  AXD  PATTERN   IX   AXIMALS  399 

in  such  a  case  is  to  Ije  sought  in  utility.  The  usefulness  of 
color  in  animate  nature  as  an  inspirer  and  satisfier  of  our  own 
ipsthetic  needs  and  capacities,  or  of  color  patterns  as  means 
whereby  we  may  distinguish  and  recognize  various  sorts  of 
animals  and  })lants,  is  a  usefulness  which  may  be  answer  ciiougii 
to  the  passing  poet  on  the  one  hand,  and  to  the  old-liiK,'  Lin- 
ncean  systematist  on  the  other,  but  it  is,  of  course,  no  answer 
to  science.  Science  demands  a  usefulness  to  the  ccjlor-bejiring 
organisms  themselves:  and  a  usefulness  large  and  seriou.s 
enough  to  be  the  sufficient  cause  for  so  highly  specialized  and 
amazing  a  development. 

The  explanations  of  some  of  the  color  i)henomena  of  animals 
are  obvious:  some  uses  we  recognize  quickly  as  certain,  some  as 
probable,  some  as  possible.  Some  colors  are  obviously  there 
simply  because  of  the  chemical  make-up  of  parts  of  the  insect 
body.  That  gold  is  yellow^  cinnabar  red,  and  certain  copper 
ores  green  or  blue,  are  facts  which  lead  us  to  no  special  in(piir.y 
after  significance:  at  least,  not  after  significance  based  on 
utility.  If  an  insect  has  part  of  its  body  composed  of  or  con- 
taining a  substance  tliat  is  by  its  very  chemical  and  i)hysical 
constitution  always  red  or  blue  or  green,  we  may  be  content 
with  knowing  that,  and  not  be  too  insistent  in  our  demand  to 
the  insect  to  show  cause,  on  a  basis  of  utility,  for  ])eing  partly 
red  or  blue  or  green.  And  even  if  this  red  or  blue  be  dis})osed 
with  some  symmetry,  some  regularity  of  repetition,  either 
segmentally  or  bilateraUy,  this  we  may  well  attribute  to  the 
natural  segmental  and  bilaterally  synnnetrical  repetition  of 
similar  body  parts.  Some  color  and  some  color  pattern,  then, 
may  be  exphcable  on  .the  same  basis  as  the  color  of  a  mineral 
specimen  or  of  a  tier  of  bricks. 

But  no  such  explanation  will  for  a  moment  satisfy  us  as 
to  the  presence  of  and  arrangement  of  colors  in  the  wings  of 
Kallima,  the  dead  leaf  butteriiy,  or  in  Plnfllium,  the  green  leaf 
phasmid,  or  in  the  butterfly  fish,  Cfuvtodon,  or  in  the  lichen 
spider,  or  in  the  chameleon  with  its  changing  tints,  or  in  any 
one  of  a  score  of  other  more  or  less  familiar  forms  whose  color 
pattern  makes,  even  on  the  casual  observer,  an  insistent 
demand  for  rational  exi)lanation. 

Certain  uses  of  color  seem  apparent:  tlie  coIohmI  eye  flecks 
or  pigment  si)ots  of  many  of  the  lower  animals  i)resumal)ly 
serve  their  possessors  as  organs  by  wliich  to  distinguish  tho 


400  EVOLUTION  AXD  ANIMAL  LIFE 

presence  or  absence  of  light,  by  virtue  of  their  capacity  to 
absorb  hght  and  thus  stimulate  the  specially  sensitive  cells 
composing  them.  And  the  pigment  or  absence  of  it  (dark 
or  light  color)  in  the  fur  and  plumage  of  certain  mammals  and 
birds  may  perhaps  serve  to  absorb  or  to  reflect  the  sun's  rays 
so  as  to  help  keep  warm  or  cool  the  animals  thus  colored.  But 
such  explanations  of  animal  colors  can  obviously  apply  to  but 
few  cases.  Very  plainly  color,  and  especially  pattern,  has  its 
significance  if  anywhere  in  connection  with  certain  special  re- 
lations of  animals  to  other  animals  and  to  the  world  generally. 
So,  ever  since  the  days  of  Darwin,  two  general  categories 
of  such  significance  or  explanation  of  color  and  pattern  have 
been  in  the  minds  of  naturalists.  One  of  these  is  the  signifi- 
cance attributed  to  color  pattern  by  the  theory  of  sexual 
selection;  the  other  is  that  attributed  to  it  by  the  general  theory 
or  group  of  theories  of  protective  resemblance,  recognition, 
warning,  directive,  and  mimetic  coloration,  etc.  Of  these  two 
general  explanations,  one  has  steadily  lost  ground  since  Dar- 
winian and  early  post-Darwinian  days,  while  the  other  has 
slowly  but  steadily  gained  adherents  and  has  been  extended  to 
cover  more  and  more  cases  of  animal  ornamentation.  Of  the 
theory  of  sexual  selection  it  must  be  said  that  it  certainly  can- 
not explain  the  conditions  of  secondary  sexual  differences, 
including  colors  and  patterns,  in  many  groups  of  animals,  and 
it  has  really  not  been  proved  to  explain  them  in  any  single 
group,  although  in  the  case  of  birds  and  mammals  it  seems 
possible  that  the  theory  is  applicable:  at  least  no  other  ex- 
planation of  equal  validity  has  yet  been  presented.  Of  the 
specialization  of  color  and  pattern  for  the  sake  of  protecting 
the  animal  by  making  it  so  harmonize  or  fuse  with  the  usual 
environment  as  to  be  indistinguishable,  or  by  making  it  simulate 
with  sufficient  fidelity  some  particular  part  of  its  surroundings 
as  a  green  or  dead  leaf,  a  twig,  the  dropping  of  a  bird,  a  bit  of 
lichen  or  what  not,  or  by  making  it  mimic  some  other  animal 
notoriously  well  defended  by  sting  or  fangs  or  ill-tasting  body, 
so  that  the  otherwise  defenseless  mimicker  is  mistaken  by  its 
enemies  for  the  defended  mimicked  kind  of  animal — of  this 
specialization  and  utility  of  color  and  pattern,  evidence  for  its 
reality  is  gradually  accumulating  to  convincing  amount.  And 
it  is  of  this  sort  of  color  and  pattern  specialization  that  the 
brief  discussion  to  follow  will  be  devoted. 


COLOR   AND   rATTKRX    IX    ANIMALS 


401 


Fin.  248. — Katydid,  Ci/rtopfij/llis  crcpitnua,  from  tin*  We.-f 
Indies,  with  green  body  and  wings  resembling  tlie  Icuve» 
among  which  it  Uves.     (After  Sharp.) 


The  green  katydid  singing  in  the  tree-top  or  sliruhhery  is 
readily  known  to  be  there  by  its  musie,  })iit  jnst  wliicli  bit  of 
green  that  we  see  is  katydid,  and  which  is  Uuif,  is  a  matter  to 
be  decided  only  by  unusually  discriminating  eyes.  The  clacking' 
locust;  beating  its 
black  wings  in  the 
air,  is  conspicuous 
enough;  but  after 
it  has  alighted  on 
the  ground  it  is 
invisible,  or, 
rather,  visible  but 
indistinguishable  : 
its  gray  and  brown 
mottled  color  pat- 
tern is  simply  continuous  with  that  of  the  soil.  The  green 
larvse  of  the  Pierid  butterflies  lying  longitudinally  along  green 
grasses  simply  merge  into  the  color  sclieme  of  their  environ- 
ment.    The  gray  moths  rest  unpereeived  on  the  bark  of  the 

tree  trunk.  Hosts  of  insect  kiiuls 
do  really  harmonize  with  the  color 
pattern  of  their  usual  environ- 
ment, and  l)y  this  correspondence 
in  shade  and  marking,  are  dilficult 
to  perceive  for  wliat  they  are. 
Now  if  the  eyes  that  survey  the 
green  foliage  or  run  over  the  gray 
bark  are  those  of  a  jireying  bird, 
lizard,  or  other  enemy,  it  is  (piitc 
certain — our  reason  tells  us  .so  in- 
sistentlv — that  this  i^ossession  bv 
the  insect  of  color  and  ])attein 
tending  to  make  it  indistinguisli- 
able  from  its  innnediate  environ- 
ment is  advantageous  to  it — ad- 
vantageous to  the  degree  often  of 
savins:  its  life.      Now  such  a  u.^^e 


'^'^^  :a>'-.'- 


Fig.  249.— Small  locust  of  the  Colo- 
rado-Mohave desert  on  the  sand. 


of  color  and  pattern  is  obviously  one  which  can  be  witlesprea<l 
through  the  insect  class,  and  may  be,  to  many  sju'cies  wliicli 
lead  lives  exposed  to  the  attacks  of  in.sectivorous  animals,  of 
large — even  of  life  and  death — importance.     And  naturalists, 


402  EVOLUTION   AND   ANIMAL   LIFE 

most  of  them  at  least,  believe  that  this  kind  of  usefulness  is 
real,  and  that  it  is  the  principal  clew  to  the  chief  significance 
of  color  and  pattern — and  this  not  alone  in  the  case  of  in- 
sects, but  of  most  other  animals  as  well. 

From  this  point  of  view,  namely,  that  color  patterns  may 
be  of  advantage  in  the  struggle  for  existence,  just  as  strength, 
swiftness,  and  other  capacities  and  conditions  are,  the  speciali- 
zation and  refinement,  all  tlie  wide  modification  and  variety 
of  colors  and  patterns  are  explicable  by  the  hypothesis  of 
their  gradual  development  in  time  through  the  natural  selec- 
tion of  fortuitous  advantageous  variations.  On  this  basis, 
such  special  instances  of  resemblance  to  particular  parts  of 
the  environment,  as  that  shown  by  Kallima  in  its  likeness 
to  a  dead  leaf,  and  Diapheromera  in  its  simulation  of  a  dry, 
leafless  twig,  are  simply  the  logical  extremes  of  such  a  line  of 
specialization. 

But  the  nature  observer  may  be  inclined  to  ask  how  such 
brilliant  and  bizarre  colors  as  those  of  the  swallowtail  butter- 
flies and  the  tiger-banded  caterpillars  of  Aiiosia  can  be  included 
in  any  category  of  "protective  resemblance"  patterns.  They 
are  not  so  included,  but  are  explained  ingeniously  by  an  added 
hypothesis  called  that  of  "warning  colors,"  while  for  the  strik- 
ing similarities  of  pattern  often  noted  between  two  unrelated 
conspicuously  colored  species  still  another  hypothesis  is  pro- 
posed. In  these  cases  it  is  not  concealment  that  the  color 
pattern  effects,  but  indeed  just  the  opposite.  Since  the  pioneer 
studies  of  Bates  and  Wallace  and  Belt,  naturalists  have  been 
observing  and  experimenting  and  pondering  these  exposing, 
as  well  as  these  concealing,  conditions  of  color  and  pattern, 
and  they  have  proposed  several  theories  or  hypotheses  ex- 
planatory of  the  vaiious  conditions.  These  hypotheses  are 
plausible;  but  they  are  much  more  than  that:  they  are  each 
more  or  less  well  backed  up  by  observation  and  experimicnt, 
and  some  of  them  have  gained  a  large  acceptance  among 
naturalists.  Both  the  reasoning  and  observed  facts  on  which 
these  hypotheses  rest  are  based  on  the  usefulness  of  the  colors 
and  patterns  to  the  animals  in  their  relation  to  the  outside  world. 
And  the  influence  of  advantage  and  natural  selection  is  given 
the  chief  credit  for  determining  the  present-day  conditions  gf 
these  colors  and  patterns. 

Before;  however,  we  take  up  these  hypotheses,  defining 


COLOR    AND   PATTiJLN    IX   ANIMALS  403 

tlicin  and  looking  over  some  of  the  evidonco  adduced  for  ilieir 
support,  as  well  as  some  of  the  criticism  leveled  at  them,  we 
may  advisedl}'  look  to  the  actual  physical  causation  of  color 
in  animals.  Whatever  the  use  or  si<^nificance  of  color,  our 
understanding  of  this  use  must  be  based  on  a  knowledge  of  the 
method  or  modes  of  its  actual  production. 

Color  in  organisms  is  produced  as  color  in  inorganic  nature 
is.  Certain  substances  have  the  capacity  of  selective  absorj)- 
tion  of  light  rays,  so  that  when  white  light  falls  on  them, 
certain  colors  (light  waves  of  certain  length)  are  al)sorbcd.  while 
certain  others  (light  waves  of  certain  other  lengths)  are  re- 
flected. An  object  is  red  because  the  substance  of  which  it  is 
(superficially)  composed,  reflects  the  rvd  rays  and  absorbs  the 
others.  Certain  other  objects  or  substances  may  produce  color 
(be  colored)  because^of  their  physical  rather  than  their  chemical 
constitution;  their  -surface  may  be  com])osed  of  superposed 
lamelke,  or  it  may  be  so  striated  or  scaled  that  the  various 
component  rays  of  white  light  are  reflected,  refracted,  and 
diffracted  in  such  varying  manner  (at  different  angles  and 
from  different  de])ths)  tliat  complex  interference  effects  are 
l):'o:laced,  resulting  in  the  practical  extinguishing  of  certain 
colo;s  (waves  of  certain  length)  or  the  reflection  of  some  at 
angles  so  as  not  to  fall  on  the  eye  of  the  observer,  and  so  on. 
Such  colors  will  change  with  changes  in  the  angle  of  observa- 
tion, and  are  the  so-called  metallic  or  iridescent  colors.  These 
two  categories  of  color  have  been  aptly  called  chemical  and 
physical:  chemical  color  depending  on  the  chemical  make-up 
of  the  body,  physical  on  its  structural  or  i)hysical  make-up. 
As  a  matter  of  fact  we  shall  find  that  most  animal  colors 
are  due  to  a  combination  of  these  two  kinds. 

(Substances  that  produce  color  by  virtue  of  their  capacity 
to  absorb  certain  colors,  and  reflect  only  certain  others,  we 
may  call,  in  our  discussion  of  color  jiroduction,  "pigments"; 
and  "pigmental"  may  be  used  as  practically  synonymous  with 
"chemical"  in  referring  to  colors  thus  produced,  while  "struc- 
tural" may  be  used  as  synonymous  with  "i)hysicar'  in 
referring  to  colors  dependent  on  superficial  structural  character 
of  the  insect  body.  For  colors  produced  by  the  co(')peration 
of  both  pigment  and  structure,  "combination"  or  "  chemico- 
physical"  may  be  used  as  a  defining  name.) 

Now  in  all  animals,  color  depends  on  the  presence  and  ar- 


i04  EVOLUTION  AND  ANIMAL  LIFE 

rangement  of  pigments  or  on  the  fine  structure  of  superficial 
partS;  as  feathers,  scales,  skin,  etc.,  or  .on  a  combination  of  the 
two  color-producing  conditions.  In  birds,  for  example,  certain 
fat  pigments  called  lipochromes  (which  are  either  actual  reserve 
food  products  or  are  associated  with  such),  are  abundantly 
present  in  the  feathers,  bill,  feet,  etc.,  producing  reds,  yellows, 
browns,  etc.,  and  certain  other  dark  melanin  pigments  are 
distributed  as  minute  amorphous  granules  in  the  cuticular 
structures  or  epidermis,  producing  plain  gray,  brown,  black, 
and  related  tints.  In  addition,  the  feathers  are  so  constructed 
that  they  may,  and  do  in  some  cases,  produce  the  most  brilliant 
iridescent  and  metallic  colors,  as  familiarly  shown  to  us  bv  the 
humming  birds,  the  grackles,  etc.  Most  such  metallic  colors 
in  birds,  how^ever,  are  produced  by  a  combination  of  pigment 
and  structure,  and  not  by  structure  alone.  The  colors  of 
mammals,  of  reptiles,  of  amphibians  and  of  fishes  might  also 
be  referred  to,  and  as  far  as  they  have  been  studied  or  analyzed 
according  to  their  causes,  we  should  find  that  in  mammals  the 
pigmental  colors  are  mostly  produced  by  so-called  melanins 
which  seem  to  be  waste  products.  In  the  fishes,  amphibians 
and  reptiles,  the  pigments  are  both  lipochromes  and  melanins, 
while  in  all  the  vertebrate  classes  there  occur  cases  in  which 
vivid  physical  or  optical  colors  are  produced  by  cuticular 
structure.  The  most  extended  study  of  color  in  animals, 
however,  has  been  devoted  to  insect  colors.  Here  we  have  a 
pretty  clear  understanding  of  all  the  color-producing  agents, 
and  an  analysis  of  aU  the  colors  more  usually  met  with,  into 
their  proper  classes,  that  is,  whether  exclusively  pigmental, 
exclusively  structural  or  mixed  structural-pigmental.  In  a 
valuable  paper  by  Tower,  a  table  of  insect  colors  showing  the 
classification  and  mode  of  production  of  the  various  colors  is 
given,  as  follows  (see  next  page) : 

The  only  hypothesis  that  gives  to  colors  and  markings  a 
value  in  the  life  of  animals,  at  all  comparable  with  the  degree 
of  specialization  reached  by  these  colors  and  markings  and  by 
the  special  structures  developed  to  make  them  possible,  is  that 
already  referred  to  as  the  theory  of  protective  and  aggressive 
resemblances,  of  warning  and  directive  patterns,  and  of  mimi- 
cry. These  various  uses  of  color  patterns  are  all  concerned 
with  the  relation  of  the  animal  to  its  environment:  they  are 
means  of  protecting  the  anii^al  from  its  enemies,  or  of  enabling 


COLOR  AND  PATTERN   IX   ANIMAL8 


405 


O 

o 


■J} 
I— I 
fa 

o 


tSo 

S2 

;~. 

i:  c 

CL  rt 

o 

C 

k> 

rH  t 

&/ 

,<^  "^ 

>i 

^   r. 

iS 

- 1: 

OS 

C 

5| 

r'. 

U 

o 

^^ 

r* 

r 

■Si 

406  EVOLUTION  AND  ANIMAL  LIFE 

it  to  captui'e  its  pre3^  They  are  uses  obviously  concerned 
wdth  the  "struggle  for  existence":  they  are  "shifts  for  a  living." 
For  the  sake  of  clearness  in  discussion  these  various  uses 
will  be  rather  arbitrarily  classified  into  several  categories  which 
in  Nature  are  not  so  sharply  distinguished  as  the  paragraph 
treatment  of  them  might  suggest. 

The  general  harmonizing  in  color  and  pattern  with  the  color 
scheme  of  the  usual  environment  is  a  condition  whicli  every 
field  student  of  animals  recognizes  as  widely  existing.  The 
green  color  of  foliage-inhabiting  forms,  as  tree  frogs  and  katy- 
dids, the  mottled  gray  and  tawny  of  the  mammals,  birds, 
hzards,  and  insects  of  the  deserts,  and  the  white  of  the  hares 
and  foxes  and  owls  and  ptarmigan  of  the  arctic  and  alpine 
snow-covered  wastes,  are  color  tones  obviously  in  harmony  with 
the  general  color  of  the  environment.  In  the  brooks  most  fishes 
are  dark  olive  or  greenish  above  and  white  below.  To  the  birds 
and  other  enemies  which  look  down  on  them  from  above,  they 
are  colored  like  the  bottom.  To  their  fish  enemies  which  look 
up  from  below,  their  color  is  like  the  white  light  above  them, 
and  their  forms  are  not  clearl}^  seen.  The  fishes  of  the  deep  sea 
in  perpetual  darkness  are  violet  in  color  below  as  well  as  above. 
Those  that  live  among  seaweeds  are  red,  grass-green,  or  olive 
like  the  plants  they  frequent.  The  difficulty  of  distinguishing 
a  quiescent  moth  from  the  bark  on  which  it  is  resting,  a  green 
caterpillar  or  leaf-hopper  or  meadow  grasshopper  from  the 
leaf  to  which  it  clings,  a  roadside  locust  from  the  soil  on  which 
it  alights,  is  a  difficulty  which  has  to  be  reckoned  with  by 
every  collector. 

Now  while  there  are  few  human  collectors  of  insects,  there 
are  hosts  of  bird  and  toad  and  hzard  insect-hunters,  to  say 
nothing  of  the  many  kinds  of  predaceous  insects  which  use  their 
o\\Ti  cousins  for  chief  food.  So  that  where  this  difficulty  of 
distinguishing  the  resting  insect  from  its  environment  is  suffi- 
cient to  postpone  success  on  the  part  of  the  insect-hunting 
bird  or  hzard,  the  life  of  the  protectively  colored  insect  is 
obviously  saved,  for  the  time,  by  its  dress.  This  is  a  utility  of 
color  and  pattern  than  which  there  can  be,  from  the  insect  point 
of  view,  nothing  higher. 

One  special  point  should  be  noted  in  connection  with  the 
general  protective  resemblance,  and  that  is,  that  the  harmon- 
izing or  melting  into  the  environment  may  often  be  accomplished 


COLOR   AND   PAITEUX   IX   ANIMATES  407 

by  a  color  and  pattern  not  directly  imitative  of  the  immediate 
environmental  objects,  but  of  such  a  kind  as  to  be  lost  among 
the  light  and  shadow  gradations  produced  by  light  shining 
through  leaves,  twigs,  etc.  Thayer  has  very  interestingly 
shown  the  possibilities  and  actual  efTects  of  such  gradatory  or 
light  and  shadow  patterns  among  l)irds,  and  thus  explains  many 
cases  of  bird  patterns  not  ai)i)arently  very  closely  imitative, 
but  nevertheless  very  effective  in  making  the  bird  indistin- 
guishable when  at  rest  on  its  nest  or  in  the  bushes  or  grass 
of  its  usual  habitat.  General  protective  resemblance  is  un- 
doubtedly very  widespread  among  animals,  and  is  not  easily 
appreciated  when  the  animal  is  seen  in  museums  or  zoc)- 
logical  gardens — that  is,  away  from  its  natural  or  normal  en- 
vironment. 

A  modification  of  general  color  resemblance  found  in  many 
animals,  may  be  called  variable  protective  resemblanc(>.  Certnin 
hares  and  other  animals  that  live  in  northern  latitudes  are 
wholly  white  during  tlie  winter  wlien  the  snow  covers  every- 
thing; but  in  summer,  when  nmch  of  the  snow  melts,  reveahng 
the  brown  and  gray  rocks  and  withered  leaves,  these  creatures 
change  color,  putting  .on  a  grayish  and  brownish  coat  of  h.-iir. 
The  ptarmigan  of  the  Rocky  IMountains  (one  of  the  grouse), 
which  lives  on  the  snow  and  rocks  of  the  high  peaks,  is  almost 
wholly  v>iiite  in  winter;  but  in  summer,  when  most  of  the  snow 
is  melted,  its  plumage  is  chiefly  brown.  Locusts  of  various 
species  of  the  genus  Trimerotropis  show  a  variability  in  color 
of  individuals,  ranging  through  gray,  brown,  reddish,  plumbeous 
and  bluish,  and  such  accompanying  variability  in  marking  as 
to  result  in  producing  much  variety  of  ai)pearance  in  a  single 
series  of  collected  individuals.  We  have  noted  in  collecting 
these  locusts  in  Colorado  and  California  that  this  variability 
of  coloration  is  directly  associated  with  color  differences  in  the 
soil  of  the  localities  in  which  these  locusts  live;  the  reddish 
individuals  are  taken  from  spots  where  the  soil  is  reddish,  the 
grayish,  where  it  is  sand-colored,  and  the  ])lumbeous  and  bluisii 
from  soil  formed  by  decomposing  bluish  rock.  Tlie  same 
variations  in  color  are  evident  in  the  horncnl  toads  (Phnjuosotna), 
as  found  on  various  colors  of  desert  soils. 

On  the  campus  of  Stanford  University  there  is  a  little  jHMid 
whose  shores  are  covered  in  some  places  with  bits  of  bluisli 
rock,  in  other  places  with  bits  of  reddish  rock^  and  in  slill 


408  EVOLUTIO^Nf   AND   ANIMAL   LIFE 

others  with  sand.  The  toad  bug  (Galgulus)  Hves  abundantly 
on  the  banks  of  this  pond.  Specimens  collected  from  the 
blue  rocks  are  bluish  in  ground  color,  those  from  the  red 
rocks  are  reddish,  and  those  from  the  sand  are  sand-colored. 
But  these  insects  have  fixed  colors  ;  they  cannot,  like  the 
chameleon  and  certain  other  lizards,  or  like  numerous  small 
fishes  and  some  tree  frogs,  change  color,  quickly  or  slowly, 
with  changes  in  position — that  is,  movements  from  green  to 
brown  or  to  other  colored  environment.  Variable  protective 
resemblance  in  insects  is,  as  far  as  known,  a  variability  directly 
induced,  to  be  sure,  by  varying  environment,  but  all  acquired 
during  the  development  of  the  individual  insects,  and  fixed  by 
the  time  they  reach  the  adult  stage.  But  changes  of  color 
to  suit  the  changing  surroundings  can  be  quickly  made  in  the 
case  of  some  animals.  The  chameleons  of  the  tropics,  whose 
skin  changes  color  momentarily  from  green  to  brown,  blackish 
or  golden,  is  an  excellent  example  of  this  highly  specialized 
condition.  The  same  change  is  shown  by  a  small  lizard  of  our 
Southern  States  (Anolis),  which  from  its  habit  is  called  the 
Florida  chameleon.  There  is  a  little  fish  (Oligocottus)  which 
is  common  in  the  tide  pools  of  the  bay  of  Monterey,  in  Cali- 
fornia, whose  color  changes  quickly  to  harmonize  with  the 
different  colors  of  the  rocks  it  happens  to  rest  above.  Most 
of  the  tree  frogs  show  this  variable  coloring. 

The  well-known  experiments  of  Trimen,  Miiller,  and  Poulton 
on  the  pupating  larvae  of  swallow-tailed  butterflies  (Papilio), 
and  of  Poulton  on  other  butterflies  of  numerous  species  with 
naked  chrysalids,  show  that  they  take  on  the  color,  or  a  shade 
resembling  it,  of  the  substance  surrounding  these  larvae.  They 
show  also  that  the  result  is  due  to  a  stimulus  of  the  skin  by  the 
enclosing  color,  and  not  to  a  stimulus  received  through  the 
eyes,  and  carried  to  the  skin  by  the  nerves.  Larvae  just  ready 
to  pupate  were  enclosed  in  boxes  lined  with  paper  of  different 
colors;  the  chrysalids  when  formed  were  found  to  be  colored  to 
harmonize  with  that  particular  shade  of  paper  by  which  they 
were  surrounded  while  pupating.  As  these  chrysalids  in  nature 
hang  exposed  on  bark  and  in  other  unsheltered  places,  without 
protecting  cocoon  or  cover  of  any  kind,  the  actual  protective 
value  of  this  harmonious  coloration  is  obvious.  It  is  a  familiar 
fact  to  entomologists  that  most  butterfly  chrysalids  and  naked 
pupae  of  moths  (unless  concealed  in  the  ground  or  elsewhere) 


COLOR   AND   PArrERX    IX    ANIMALS 


4()9 


Fio,  250. — Chrj-salid  of  swallowtail 
butterfly,  Papi7«o,  which  cIo(*<'Iy  re- 
sembles the  bark  on  which  it  rej*!.-*. 


resemble  in  color  and  general  external  appearance  the  surface 

of  the  object  on  which  they  rest.     The  chrysalids  of  various 

Papilios  are   indeed   marveloiisly 

faithful     imitations    of     bits    of 

rough  bark  (Fig.  250).- 

The    larvffi    (caterpillars)     of 

various  moths,  particularly  Geo- 

metrid     and     Sphingid     species, 

often  appear  in  two  color  types, 

one  brown  and  the  other  green. 

Poulton   has    shown    by    experi- 
ment and  observation  with  some 

of  these  species  that  those  larva) 

reared   among   green   leaves  and 

twigs  become  green,  while  those 

on  dry  branches  become  brown. 

This    variable    protective   reseml)lance,  like   that  of    Trimrro- 

tropis,  Galgulus,  and  the  Papilio  chrysalids,  also  is  fixed  aftc  i- 

being  once  acquired. 

An  interesting  exam])le  of 
color  harmony  which  may  bo 
classified  under  the  head  of 
variable  protective  resem- 
blance is  that  of  the  larva?  of 
Lycoena  sp.,  abundant  on  the 
flower  heads  of  the  California 
buckeye,  ^€sculiis  cahforniciis, 
that  blooms  in  May.  Tlie  butis 
of  the  buckeye  are  green,  or 
gi'een  and  rose,  or  even  all 
rose  externally.  Tlie  (juiet 
sluglike  Lycirnid  hirvu'  lie 
longitudinally  along  the  buds 
and  their  short  stems,  and 
are  either  green  with  faint 
rose  tinge,  esj^ecially  along 
the  middle  of  the  back,  or 
are  distinctly  rosy  all  over, 
depending    strictly    uj)<»n    tlu^ 

color  tone  of  the  particular  branch  serving  as  their  habitat. 

The  correspondence  in  shade  of  color  is  strikingly  exact:  the 


Fig.  2r)l. — Two  ortliopterous  leaf  hoppers 
or  membraoids:  'llie  iipi)er  one.  Xtro- 
phyllum  simile:  the  lower  one,  Clndo- 
notus  humbcrtimus.     (.\fter  BoHvar.) 


410 


EVOLUTION  AND  ANIMAL  LIFE 


Fig,  252. — The  mousefish,  Pterophryne  histrio,  in  the  Sargassum  or  Gulf  weed.  The 
fishes  are  marked  and  colored  so  as  to  be  nearly  indistinguishable  from  the  mass  of 
the  Gulf  weed.  In  the  lower  right-hand  corner  of  the  figure  are  two  seahorses,  also 
shaped  and  marked  so  as  to  be  concealed. 


COLOR  AND  PATTERN  IN  ANIMALS 


411 


utter  indistinguisliability  of  the  larvae  is  something  that  needs 
to  be  experienced  to  be  fairly  realizcHJ. 

Far  more  striking  are  those  cases  of  protective  resemblance 
in  which  the  animal  re- 
sembles in  color  and  sha])e, 
sometimes  in  extraordi- 
nary detail,  some  partic- 
ular ol)jcct  or  i)art  of  its 
usual  environment.  Cer- 
tain parts  of  the  Atlantic 
Ocean  are  covered  with 
great  patches  of  seaweed 
called  the  Gulf  weed  {S(ir- 
gassum),  and  many  kinds 
of  animals  —  fishes  and 
other  creatures — live  upon 
and  among  the  algic.  No 
one  can  fail  to  note  the 
extraordinary  color  resem- 
blances which  exist  be- 
tween these  animals  and 
the  weed  itself.  The  gulf 
weed  is  of  an  olive-yellow 
color,  and  the  crabs  and 
shrimps,  a  certain  flat- 
worm,  a  certain  mollusk, 
and  certain  httle  fishes, 
all  of  which  live  among 
the  Sargassiirn,  are  exactly 
of  the  same  shade  of  yel- 
low as  the  weed,  and  have 
small  white  markings  on 
their  bodies  which  are 
characteristic  also  of  the 
Sargassum.  The  mouse- 
fish  and  the  little  sea- 
horses,  often   attached   to 

the  Gulf  weed,  show  the  same  trails  of  coloration  (Tig.  2.'/J). 
The  slender  grass-green  caterpillars  of  many  moths  and  butter- 
flies resemble  very  closely  the  thin  grass  blades  among  which 
they  Uve.    The  larvae  of  the  geometrid  moths,  called  inchwgniiii 


Fig.  253. — A  ripomelrid  Inn'a  on  ft  oranoh. 
(The  larva  !.•<  tlic  upper  riRht-hnixI  projection 
from  the  twig.) 


412 


EVOLUTION  AND  ANIMAL  LIFE 


or  spanworms,  are  twiglike  in  appearance,  and  have  the  habit, 
when  disturbed,  of  standing  out  stiffly  from  the  twig  or  branch 
upon  which  they  rest,  so  as  to  resemble  in  position  as  well  as 
in  color  and  markings  a  short  or  a  broken  twig.     One  of  the 


Fig.    254. — The  walking-stick  insect, 
Diapheromera  femorata,  on  twig. 


Fig.  255. — A  twig-simulating 
insect  from  Samoa.  (From 
specimen.) 


most  striking  resemblances  of  this  sort  is  show^n  by  the  large 
geometrid  larva  illustrated  in  Fig.  253,  which  was  found  near 
Ithaca,  New  York.  The  body  of  this  caterpillar  has  a  few  small, 
irregular  spots  or  humps,  resembling  very  closely  the  scars  left 
by  fallen  buds  or  twigs.  These  caterpillars  have  a  special  mus- 
Qular  development  to  enable  them  to  hold  themselves  rigidly 


COLOR   AND   PATTERN    IX   ANIMATE 


413 


for  long  times  in  tliis  trying  attitude.  Tliey  also  laek  the 
middle  proplegs  of  the  body,  common  to  other  le})idopterou.s 
larva},  the  jn-esence  of  ^vhit']l  would  tend  to  destroy  tlie  illus'T 
so  successfully  carried  out  by  them.  The  common  walking 
stick  (Di(iphcromera)  (Vig.  254),  with  its  wingless _  greatly 
elongate,  dull-colored  l)ody,  is  an  excellent  example  of  special 
protective  resemblance.  It  is  quite  indistinguisha))le,  when  at 
rest,  from  the  twigs  to  which 
it  is  clinging.  Another  member 
of  the  family  of  insects  to  which 
the  walking  stick  Ijelongs  is  the 
famous  green-leaf  insect  {Phijl- 
lium)  (Fig.  256).  It  is  found 
in  South  America  and  is  of 
a  bright  green  color,  with  broad 
Icaflike  wings  and  body  with 
markings  which  imitate  the  leaf 
veins,  and  small  irregular  yel- 
lowish spots  which  mimic  decay- 
ing or  stained  or  fungus-covered 
spots  in  the  leaf. 

There  are  many  butterflies 
that  resemble  dead  leaves.  All 
our  common  meadow  browns 
(Grapta),  brown  and  reddish 
butterflies  with  ragged -edged 
wings,  that  appear  in  the  autumn 
and  flutter  aimlessly  about  ex- 
actly   like    the     falhng    leaves, 

show  this  resemblance.  But  most  remarkable  of  all  is  a  large 
butterfly  (Kallwia)  (Fig.  257)  of  the  East  Indian  region.  The 
upper  sides  of  the  wings  are  dark,  with  jnu-plish  and  orange 
markings,  not  at  all  resembling  a  dead  leaf.  But  the  butter- 
flies wiien  at  rest  hold  their  wings  together  over  the  back, 
so  that  only  the  under  sides  of  the  wings  are  exj)osed.  The 
under  sides  of  Kallima's  wings  are  exactly  the  color  of  a  dead 
and  dried  leaf,  and  the  wings  are  so  heUl  that  all  combine  to 
mimic  with  extraordinary  fidelity  a  dead  leaf  still  attached  to 
tlie  twig  by  a  short  pedicle  or  leaf-stalk  imitated  by  a  sliort  tail 
on  the  hind  wings,  and  sliowing  midrib,  obliipie  veins,  and, 
most  remarkable  of  all,  two  ai)parent  holes,  like  those  made 


Fig.  256. — The  p'c:»n-lcaf  iiKsect, 
Pltyllium. 


414 


EVOLUTION   AND   ANIMAL   LIFE 


in  leaves  by  insects,  but  in  the  butterfly  imitated  by  two  small 
circular  spots  free  from  scales  and  hence  clear  and  transparent. 
With  the  head  and  feelers  concealed  beneath  the  wings,  it  makes 
the  resemblance  wonderfully  exact. 


Fig.  257. — Kallima,  the  "dead-leaf  butterfly.'* 


The  moths  of  the  genus  Cymatophora,  and  their  larva?  also, 
mostly  harmonize  excellently  with  the  gray  bark  on  which  they 
rest,  the  moths  adding  to  their  general  simulation  the  curioii: 
habit  of  resting,  often  with  folded  Vvings,  at  an  angle  of  foruy^ 
five  degrees  with  the  tree  trunk,  head  downward,  with  the 
curiously  blunt  and  uneven  wing  tips  projecting,  so  as  to  imitate 


COLOR   AND   PATTERN   IN   ANIMATES 


■llo 


with  great  fidelity  a  short  broken- 
off  brancli  or  chip  of  bark.  Nu- 
merous other  moths  and  caterpil- 
lars resemble  bark  and  habitually 
rest  on  it.  Catocala,  Schizura, 
and  other  genera  furnish  ex- 
amples familiar  to  the  moth  col- 
lector. 

.here  are  numerous  instancop; 
Oi  s^ -.^ial  protective  resemblance 
among  spiders.  Many  spiders 
that  live  habitually  on  tree 
trunks  resemble  bits  of  bark  or 
small,  irregular  masses  of  lichen. 
A  whole  family  of  spiders,  wliich 
live  in  flower  cups  lying  in  wait 
for  insects,  are  VNiiite  and  pink 
and  particolored,  resembling  the 
markings  of  the  special  flowers 
frequented  by  them.  This  is,  of 
com-se,  a  special  resemblance  not 
so  much  for  protection  as  for  ag- 
gi'ession;  the  insects  coming  to 
visit  the  flowers  are  unable  to 
distinguish  the  spiders  and  fall 
an  easy  prey  to  them. 

Any  field  student  of   insects, 
b}^  paying  attention  to  the  matter  of  .-^iiecial  j^rotective  resem- 
blance, C{?n  soon  make  up  a  striking  list  of  examples.     Some 
of  these  may  be  more  convincing  to  him  than  to  persons  soe- 
^.*—  ing  his  si>eoimons 

Hi  11 "'"^^    —  i^    t^^c   c()l'ectinj« 

^•^^^^^jMM^^  ])oxes,  and   sonic 

V.   .;':'"  "\  indee«l  will   jirol)- 

'l^fci.  ij^jK  ably     be      qucs- 

^"^^^^''^^^«:^  tioned    by    closet 

natundists.  liut 
nevertheless  no 
collector   or   field 

Ft3.  259.— A  pipefish,  PA2///o/)/m/.r,  wliich  resembles  the  st'U-      J     .         , 

weed  amoiiK  wliich  it  Uvea.  f-.  iI.mI      to     llotC 


Fig,  2o8. — An  insect.  Gonqi/lua gonfr*/- 
loidcs,frnin  the  1-ast  Inches,  wh;th 
rests  on  the  branches  of  a  bush  re- 
sembling the  rosebush,  the  leaves 
of  which  are  closely  sinjulate<l  by 
the  body  of  the  insect.  (After 
Shar]'-) 


416  EVOLUTION   AND  ANIMAL  LIF15 

many  examples  of  this  clever  artifice  of  Nature  to  protect  her 
children. 

If  the  field  student  may  be  relied  on  to  note  and  record  a 
long  list  of  insects  colored  and  marked  so  as  to  harmonize  well 
with  their  general  environment  or  with  some  specific  part  of  it, 
he  may  also  be  relied  on  to  bring  in  a  list  of  opposites:  a  record 
of  bizarre  and  conspicuous  forms,  colored  with  brilliant  blues 
and  greens  and  streaked  and  spotted  in  a  manner  utterly  at 
variance  and  in  contrast  with  the  foliage  or  soil  or  bark  or  Avhat- 
ever  is  the  usual  environment  of  the  insect.  The  great  red- 
brown  monarch  butterfly  and  its  black-striped  green  and 
yellowish  larva,  the  tiger-banded  swallowtails,  the  black  and 


Fig.  260. — Ladybird  beetles,  conspicuously  colored  and  marked. 

yellow  wasps  and  bees,  the  ladybird  beetles  wdth  their  sharply 
contrasting  colors,  the  brilliant  gi'een  blister  beetles,  the  striped 
and  spotted  chrysomelids  —  in  all  these  and  many  others 
there  can  be  no  talk  of  protective  resemblance.  If  only  such  a 
paradoxical  theory  as  protective  conspicuousness  could  be 
established,  then  these  colors  and  markings  might  well  be 
explained  by  it. 

Exactly  such  an  explanation  of  brilliant  color  and  contrast- 
ing markings  is  afforded  b}^  the  theory  of  warning  colors.  It 
has  been  conclusively  sho\Mi,  by  observation  and  experiment 
by  several  naturalists,  that  many  insects  are  distasteful  to 
birds,  lizards,  and  other  predaceous  enemies.  This  is  so  be- 
cause the  blood  lymph  or  some  specially  secreted  body  fluid  of 
these  insects  contains  an  acrid  or  ill-tasting  substance  so  that 
birds  -will  not,  if  they  can  recognize  the  kind  of  insect,  make 
any  attempt  to  catch  or  eat  one.      This  letting   alone   is  un- 


COLUK    AM)    PATTKitX    L\    AMMAI.h  417 

doubtedly  tlie  result  of  ])rcvi()iisly  made  (rials;  tliat  is,  it  has 
been  learned  by  experience.  Now  it  would  obviously  l>e  of 
advantage  to  those  species  of  insects  that  arc  ill-tasliriK,  if 
their  coloring  and  pattern  were  so  distinctive  and  conspicuoui; 
as  to  make  them  readily  known  by  birds,  and  once  learned 
easily  seen.  A  distasteful  cateri)illar  needs  to  advertise  it:: 
mipalatability  so  effectively  that  the  swooping  bird  will  recog- 
nize it  before  making  that  single  sharp-cutting  stroke;  or  peck 
that  would  be  as  fatal  to  a  caterpillar  as  being  wholly  eaten. 
Hence  the  need  and  the  utility  of  warning  colors.  And  indeed 
the  distasteful  insects,  as  far  as  recogniz{>d,  are  mostly  of  con- 
spicuous colors  and  patterns. 

Such  warning  colors  are  presumably  possesserl  not  only  by 
unpalatable  insects,  but  also  by  many  that  have  certain  sj)ecial 
means  of  defense.  The  wasps  and  bees,  provided  with  stings 
dangerous  to  most  of  their  enemies,  are  almost  all  conspicu- 
ously marked  with  yellow  and  l)lack.  Many  bugs,  well  defended 
by  sharp  beaks,  possess  a  conspicuous  color  ])attern. 

Numerous  other  animals  l)esides  insects  also  are  ])elieved 
to  have  warning  colors.  The  Gila  monster  {11  cinder  ma) ,  the 
only  poisonous  lizard,  differs  from  most  other  lizards  in  being 
strikingly  patterned  with  black  and  brown.  Some  of  the  ven- 
omous snakes  are  conspicuousl}^  colored,  as  the  coral  snakes 
(Flaps)  or  coralillos  of  the  tropics.  The  naturalist  l^elt.  whose 
observations  in  Nicaragua  have  added  much  to  our  knowledge 
of  tropical  animals,  describes  as  follows  an  interesting  exanii)le 
of  \varning  colors  in  a  species  of  frog: 

''In  the  woods  around  Santo  Domingo  (Nicaragua)  there  arc  many 
frogs.  Some  are  green  or  brown  and  imitate  green  or  dotul  l.vives, 
and  live  among  foliage.  Others  are  dull  earth-colored,  and  hi'lv  va 
holes  or  under  logs.  All  these  come  out  onl\-  :i1  night  to  feed,  and  tliey 
are  all  preyed  upon  by  snakes  and  l)ir(ls.  In  contrast  with  these  ol>- 
scurely  colored  species,  another  little  frog  hops  about  in  the  daytime, 
dressed  in  a  bright  livery  of  red  and  blu<'.  Ih'  cannot  l)e  mistaken  for 
any  other,  and  his  flaming  breast  and  blue  stockings  show  that  )ie  diH-s 
not  court  concealment.  He  is  very  abundant  in  th<>  (lam|)  woods,  aiul 
I  was  convinced  he  was  uneatable  so  soon  as  I  made  his  ac<iuaintanco 
and  saw  the  hajipy  sense  of  security  with  which  lie  hopped  aimut.  I 
took  a  few  specimens  home  witli  me,  and  tried  my  fowls  and  duck.s 
with  them,  but  none  would  touch  then).     M  h<\ .  by  throwing  down 


418 


EVOLUTION   AND   ANIMAL   LIFE 


pieces  of  meat,  for  which  there  was  a  great  competition  among  them, 
I  managed  to  entice  a  yomig  duck  into  snatching  up  one  of  the  httle 
frogs.  Instead  of  swallowing  it,  however,  it  instantly  threw  it  out  of 
its  mouth,  and  went  about  jerking  its  head,  as  if  trying  to  throw  off 
some  unpleasant  taste." 


Fig.  261. — A  "tobacco-worm,"  larva  of  the  sphinx  moth, 
Phlegethontius  Carolina,  showing  terrifying  attitude. 


Certain  other  insects  which  are  without  special  means  of 
defense  and  are  not  at  all  formidable  or  dangerous,  are  yet  so 
marked  or  shaped  and  so  behaved  as  to  present  a  curiously 
threatening  appearance.  The  large  green  caterpillars  of  the 
sphinx  moths  have  a  curious  rearing-up  habit  which  seems  to 

simulate  threatened 
attack  (Fig.  261). 
They  have,  too,  a 
great  pointed  spine 
or  horn  on  the 
back  of  the  pos- 
terior tip  of  the 
body  which  has  a 
most  formidable 
appearance,  but  is, 
as  a  matter  of  fact,  not  at  all  a  weapon  of  defense,  being  quite 
harmless.  Numerous  stingiess  insects,  wdien  disturbed,  wave 
about  the  hind  part  of  the  body  or  curl  it  over  or  under,  much 
as  stinging  insects  do,  and  seem  to  be  threatening  to  sting. 
The  striking  eye  spots  of  many  insects  are  believed  by  some 
entomologists  to  be  of  the  nature  of  terrifying  markings.  Mar- 
shall tried  feeding  baboons  a  full-grown  larva  (about  seven 
inches  long)  of  the  sphinx  moth,  Chcerocampa  osiris.  The 
larva  has  large  strongly  colored  eye  spots  and  is 

"  remarkably  snakelike,  the  general  coloring  somewhat  recalling  that 
of  the  common  puff-adder,  Bitis  arietans.  The  female  baboon  ran  for- 
ward expecting  a  titbit,  but  when  she  saw  what  I  had  brought  she 
flicked  it  out  of  m}^  hand  on  to  the  ground,  at  the  same  time  jumping 
back  suspiciously:  she  then  approached  it  very  cautiously,  and  after 
peering  carefully  at  it  at  the  distance  of  about  a  foot  she  withdrew  in 
alarm,  being  clearly  much  impressed  by  the  large  blue  eyelike  mark-^ 
ings.  The  male  baboon,  which  has  a  much  more  nervous  tempera- 
ment, had  meanwhile  remained  at  a  distance  survejdng  the  proceedings, 
so  I  picked  up  a  caterpillar  and  brought  it  towards  them,  but  they 


COLOR   AND   PATTKUX    IX    ANIMALS  4iy 

would  not  let- me  approach,  and  kept  runninj;  away  round  and  round 
their  pole,  so  I  threw  the  insect  at  them.  Tlicir  frijrht  was  ludicrous 
to  see;  with  loud  cries  they  jumped  aside  and  clamljered  up  the  poleaa 
fast  as  they  could  go,  into  their  ])ox,  where  they  sat  peering  rivc-r  the 
edge  watching  the  uncanny  object  below."     (Marsliall.) 

Marshall  also  writes  concerning;  the  niarkintrs  on  the  wings 
of  the  mantis,  Pseudccrcohotra  ivahlberyi : 

"They  are,  I  think,  almost  certainly  of  a  terrifying  character.  W  lien 
the  insect  is  irritated,  the  wings  are  raised  over  its  back  in  .sucIj  a 
manner  that  the  tegmina  stand  side  by  side,  and  the  markings  on  them 
present  a  very  striking  resemblance  to  the  great  yellow  eyes  of  a  l)ird 
of  prey  or  some  feline  animal,  which  might  well  deter  an  insectivorous 
enemy.  It  is  noticeable  that  the  insect  is  always  careful  to  keej)  tlie 
wings  directed  toward  the  point  of  attack,  and  this  is  often  done  witli- 
out  altering  the  position  of  the  body." 

Still  another  use  is  believed  by  some  entomologists  to  be 
afforded  by  such  markings  as  ocelli  and  other  specially  con- 
spicuous spots  and  flecks  on  the  wings  of  butterflies  and  moths, 
and  by  such  apparently  useless  parts  as  the  "tails"  of  the  hind 
wdngs  of  the  sv/allowtail,  and  Lycanid  butterflies,  and  others. 
Marshall  occupied  himself  for  a  long  time  with  collecting  butter- 
flies which  had  evidently  been  snapped  at  by  1)irds  (in  some 
cases  the  actual  attack  being  observed)  and  suffered  the  loss  of 
a  part  of  a  wing.  Examining  these  specimens  when  brought 
together,  Poulton  and  Marshall  noted  that  the  "great  majority 
[of  these  injuries  to  the  wings]  are  inflicted  at  the  anal  angle 
and  adjacent  hind  margin  of  the  hind  wing,  a  considerable 
number  at  or  near  the  apical  angle  of  the  fore  wing,  and  com- 
paratively few  between  the  points.''  In  tliis  fact,  couple«l  with 
the  fact  that  the  apical  and  hind  angles  of  tlie  fore  and  lund 
wings  respectively  are  precisely  those  regions  of  the  wings  most 
usually  specially  marked  and  ])rolonged  as  angular  j )roce.'^se.s  or 
tails,  Poulton  sees  a  s])ecial  significance  in  the  j^at terns  of  tlu\<o 
wing  parts.  He  thinks  they  are  "directive  marks  whicli  tend 
to  divert  the  attention  of  an  enemy  from  more  vital  parts." 
It  is  obvious  that  a  butterfly  can  \(My  well  afford  to  lo.<o  the 
tip  or  tail  of  a  wing  if  that  loss  will  save  losing  head  or  alKlomen. 
Poulton  sees  a   "remarkable  resemblance  of  the   marks  and 


4l>0 


EVOLUTION   AND  ANIMAL  LIFE 


structures  at  the  anal  angle  of  the  hind  vving,  under  side,  in 
many  Lyccsnidce,  to  a  head  with  antenna  and  eyes/^  and  recalls 
that  this  has  been  independently  noticed  by  many  other  ob- 
servers. The  movements  of  the  hind  wings  by  which  the  tails, 
which  appear  like  antennae,  are  made  continually  to  pass  and 
repass  each  other,  add  greatly  to  this  resemblance. 

Very  many  species  of  animals,  especially  among  the  verte- 
brates, possess  certain  distinctive  and  striking  markings,  which 


L 


■V} 
-    I 


Fig.  262. — The  butterfly  fish,  Chcetodon  vagabundus.  from  Samoa.     This  small  fish  is 

most  strikingly  colored. 


have  been  supposed  to  serve  as  recognition  marks  to  other 
animals  of  the  same  species.  In  this  theory,  these  marks  afford 
a  swift  means  of  knowing  friends  from  enemies.  Of  this 
nature  are  the  white  tufts  at  the  tail  of  the  cottontail  rabbit, 
the  black  patch  of  the  blacktail  deer,  the  flanks  of  the  Rocky 
^lountain  antelope,  the  concealed  scarlet  crest  of  the  kingbird, 
the  fiery  shoulder  of  the  redwing  blackbird,  the  blue  speculum 
of  the  duck,  the  black  bars  and  eye  spots  of  the  butterfly  fishes 
{Chcetodon),  and  the  peculiar  marks  of  one  form  or  another 
on  a  host  of  mammals,  birds,  reptiles,  and  fishes. 

It  is  very  easy  to  indicate  recognition  marks.  Keeler,  am.ong 
others,  has  given  an  elaborate  list  of  the  principal  cases  among 
American  birds,  and  there  is  scarcely  a  species  without  one  or 


COLOR   AND  PATTERN*    IN   ANIMALS  421 

more.  Nevertheless  we  are  not  sure  that  many,  or  even  any 
of  them,  actually  serve  the  purpose  of  recognition  among  the 
animals  themselves,  however  convenient  tliey  may  he  to  us 
who  study  them.  However  i)lausil)le  the  theory  of  recognition 
marks  may  seem,  it  is  still  not  proved  to  have  any  oLjective 
basis. 

Of  all  the  theories  accounting  for  the  utility  of  col^r  and 
pattern,  that  of  mimicry  demands  at  first  thought  the  largest 
degree  of  credulity.  As  a  matter  of  fact,  however,  the  olxserva- 
tion  and  evidence  on  which  it  rests  are  as  convincing  as  are  tho.sc 
for  almost  any  of  the  other  forms  of  protective  color  i)attern. 
Although  the  word  "mimicry"  could  often  have  been  uset' 
aptl}"  in  the  account  of  special  protective  resemblance,  it  lia.s 
been  reserved  for  use  in  connection  with  a  specific  kind  of 
imitation;  namely,  the  imitation  by  an  otherwise  defenseless 
insect,  one  without  ])oison,  l)eak,  or  sting,  and  without  acrid 
and  distasteful  body  fluids,  of  some  other  specially  defended  or 
inedible  kind,  so  that  the  mimicker  is  mistaken  for  the  mimicked 
form  and,  like  this  defended  or  distasteful  form,  relieved  from 
attack.  Many  cases  of  this  mimicry  may  be  noted  by  any 
field  student  of  entomology. 

Buzzing  about  flowers  are  to  be  found  various  kinds  of  bees, 
and  also  various  other  kinds  of  insects  thoroughly  beelike  in 
appearance,  but  in  reality  not  bees  nor,  like  them,  defended 
by  sting.  These  bee  mimickers  are  mostly  flies  of  various 
famihes  {Syrphidce,  Asilidce,  Bomhi/Iikhv),  and  their  resem- 
blance to  bees  is  sufficient  to  and  does  constantly  deceive 
coUectors.  We  presume,  then,  that  it  e(iually  deceives  l)irds 
and  other  insect  enemies.  Wasps,  too,  are  mimicked  l)y  other 
insects;  the  wasplike  flies,  ConopicUv,  and  some  of  the  clear- 
winged  moths,  Sesiidce  are  extremely  wasplike  in  general 
seeming. 

The  distasteful  monarch  butterfly,  Anosia  plvxippu^,  widt^ 
spread  and  abundant — a  successful  butterfly,  whose  success 
undoubtedly  largely  dejiends  on  its  inedibility  in  both  larval  and 
imaginal  stages — is  mimicked  with  extraordinary  fldelity  of  tletail 
by  the  viceroy,  Basilarchia  archippus  (Fig.  2r);5).  The  liasil- 
archias,  constituting  a  genus  of  numerous  si)ecies,  are  with  but 
two  or  three  exceptions  not  at  all  of  the  color  or  i)attern  of 
Anosia,  but  in  the  case  of  the  i)articiflar  species  archippm, 
not  only  the  red-brown  ground  color,  but  the  fine  pattern 
2a 


4l>2 


EVOLUTION   AND  ANIMAL  LIFE 


Fig.  263. — The  mimicking  of  the  inedible  monarch  butterfly  by  the  edible  viceroy. 
The  figure  at  the  top  is  the  monarch,  Anosi-a.  plexippus.  The  middle  figure  is  the 
viceroy,  Bnsilnrchia  archippus.  The  lowest  figure  is  another  member  of  the  same 
genus,  Basilarchia,  to  show  the  usual  color  pattern  of  the  species  of  the  genus. 


COLOR   AND   PATTERN    IX    AXIMaI^  423 

details  in  black  and  whitish,  copy  faithfully  the  details  in  Annsia; 
only  in  the  addition  of  a  thin  hiackisli  line  across  the  discal  area 
of  the  hind  wings  does  mrhijjpus  show  any  ncjticeahle  difTereiice. 
The  viceroy  is  believed  not  to  be  distasteful  to  birds,  but  its 
close  mimicry  of  the  distasteful  monarch  un(l()ui)tediy  leads 
to  its  being  constantly  mistaken  for  it  by  the  birds  and  thus 
left  unmolested. 

The  subject  of  mimicry  has  not  l^een  studied  largely  among 
the  insects  of  our  countrv,  but  in  the  tropics  and  subtropics 
numerous  striking  exam|)les  of  mimetic  forms  have  been  noted 
and  written  about.  The  members  of  two  large  families  of  ))utter- 
flies,  the  Danaida  and  ]feliconida»,  are  distasteful  to  birds, 
and  are  mimicked  by  many  species  of  other  butterfly  families, 
especially  the  Pierida*,  and  by  the  swallowtails,  I*apili()ni(he. 
Many  plates  illustrating  such  cases  have  l)een  j)ublished  by 
Poulton  and  Marshall,  Haase,  Weismann,  and  others.  Shelford, 
in  an  extended  account  of  mimicry  as  exenij)hfie(l  among  the 
insects  of  Borneo,  refers  to  and  illustrates  many  striking  ex- 
amples among  the  beetles,  the  Hemii)tera,  Diptera,  Orthoptera. 
Neuroptera,  and  moths;  distasteful  Lycid  beetles  are  closely 
mimicked  b}''  other  beetles,  by  Hemii)tera,  and  by  nM>tlis: 
distasteful  ladvbird  beetles  are  mimicked  bv  Hemiptera. 
Orthoptera,  and  by  otiier  beetles;  stinging  Hymenoptera  arc 
mimicked  b}^  stingless  Hymeno})tera,  by  beetles,  flies,  Ijugs. 
and  moths.  Poulton  and  ^larshall,  in  tlieir  account  of  mimicry 
among  South  African  insects,  publish  manv  colored  plates 
revealing  most  striking  resemblances  between  insects  well 
defended  by  inedibility  or  defensive  wea})ons,  and  their  mim- 
ickers.  Our  space  unfortunately  prevents  any  specific  con- 
sideration of  these  various  interesting  cases. 

The  special  conditions  under  which  mimicry  exists  have  Ihk^ii 
seriously  studied  and  are  of  extreme  interest.  It  is  obvious  that 
the  inedible  or  defended  mimicked  form  nnist  be  more  abundant 
tlian  the  mimicker,  so  that  the  experimenting  yotmg  bird  or 
lizard  may  have  several  chances  to  one  of  getting  an  ill  iiiMc 
or  a  sting  when  he  attacks  an  insect  of  certain  type  or  pattern. 
This  requirement  of  relative  abundance  of  mimicker  and 
mimicked  seems  actually  met,  as  i^roved  by  observation.  In 
some  cases  only  females  of  a  sjiecies  indulge  in  mimicry,  the 
males  being  unmodified.  This  is  exi)lained  on  the  ground  of 
the  particular  iiecc.Si:^)'  Iqi'  protection  of  the  egtr-ladcn,  heavy- 


424  EVOLUTION   AND   ANIMAL  LIFE 

fl}dng,  long-lived,  and  hence  more  exposed  females,  as  compared 
with  the  lighter,  swifter,  short-lived  males. 

It  has  been  found  that  individuals  of  a  single  species  may 
mimic  several  different  species  of  defended  insects,  this  poly- 
morphism of  pattern  existing  in  different  localities,  or  indeed 
in  a  single  one.  Marshall  believes  that  seasonal  polychromat- 
ism  of  certain  butterfly  species  is  associated  with  the  mimicry 
of  certain  defended  butterflies  of  different  species,  these  different 
species  appearing  at  different  times  of  the  j^ear. 

It  is  needless  to  say  that  such  hypotheses  and  theories  of 
the  utility  of  color  and  pattern  have  been  subjected  to  much 
criticism,  both  adverse  and  favorable.  The  necessity  for  limiting 
results  within  the  working  range  of  efficient  causes  has  been 
the  soundest  basis,  in  our  judgment,  for  the  adverse  criticism 
of  the  theories  of  special  protective  resemblance,  warning 
colors,  and  mimicry.  Until  recently  most  of  the  observations 
on  which  the  theories  are  based  have  been  simph^  observations 
proving  the  existence  of  remarkable  similarities  in  appearance  or 
equally  striking  contrasts  and  bizarrerie.  The  usefulness  of 
these  similarities  and  contrasts  had  been  deduced  logically, 
but  not  proved  experimentally  nor  by  direct  observation.  In 
recent  years,  however,  a  much  sounder  basis  for  these  theories 
has  been  laid  by  experimental  work.  There  is  now  on  record 
a  large  amount  of  strong  evidence  for  the  validity  of  the  hypoth- 
esis of  mimicry.  Certainly  no  other  hypothesis  of  equal 
validity  with  that  of  protective  resemblance  and  mimicry  has 
been  proposed  to  explain  the  numerous  striking  cases  of  similar- 
ity and  the  significant  conditions  of  life  accompanying  the  ex- 
istence of  these  cases,  which  have  been  recorded  as  the  result 
of  much  laborious  and  indefatigable  study  by  certain  naturalists. 

Plateau  and  Wheeler  have  tasted  so-called  inedible  and 
distasteful  insects  and  found  nothing  particularly  disagreeable 
about  them.  But  as  Poulton  suggests,  the  question  is  not  as 
to  the  palate  of  Plateau  and  Wheeler  nor  of  any  man;  it  concerns 
the  taste  of  birds,  lizards,  etc.  Better  evidence  is  that  afforded 
by  actual  observation  of  feeding  birds  and  lizards;  of  experi- 
mental offering  under  natural  conditions  of  alleged  distasteful 
insects  to  their  natural  enemies.  Marshall's  observations  and 
experiments  on  the  point  are  suggestive  and  undoubtedly 
reliable.     Much  more  work  of  the  same  kind  is  needed. 

The  efficient  cause  for  bringing  color  and  pattern  up  to  such 


COLOR   AND  TATTERX    IX   AXIMAL9  42o 

a  high  dcgee  of  speciahzatiou  lias  been  assiiinod,  by  nearly  all 
upholders  of  the  use  hypotheses,  to  l)e  natural  selection.  This 
agent  can  account  for  i)uri)()sefulness,  which  is  obviously  an 
inherent  part  of  all  the  hypotlieses.  And  no  other  su^^ested 
agent  can.  Weismann  makes,  indeed,  of  this  fact,  ))y  inverting 
the  problem,  one  of  the  most  efifective  arguments  for  the  potency 
and  " Allmacht"  of  natural  selection.  He  declares  tliat  tbfc 
existence  of  special  })rotective  resemblanc(%  warning  colois, 
and  mimicry  proves  the  reality  of  selection.  But  it  must  Ikj 
asked,  while  admitting  the  cogency  of  much  of  the  argument 
for  natural  selection  as  the  eflicient  cause  of  high  speciaHzation 
of  color  and  pattern  as  we  have  seen  it  actually  to  exist,  how 
such  a  condition  as  that  shown  by  the  mimicking  viceroy  butter- 
fly has  come  to  be  gradually  developed — gradual  (h'velopment 
being  confessedly  selection's  only  mode  of  working.  Could  the 
viceroy  have  had  any  protection  for  itself,  any  advantage  at  all, 
initil  it  actually  so  nearly  resembled  the  inedil)le  monarcli  a3 
to  be  mistaken  for  it?  No  slight  tinge  of  brown  on  the  black 
and  white  wings  (the  typical  color  scheme  of  the  genus),  no 
slight  change  of  marking,  would  be  of  any  service  in  making 
the  viceroy  a  mimic  of  the  monarch.  The  whole  leap  from 
typical  Basilarchia  to  (apparently)  typical  Anosia  had  to  1x3 
made  practically  at  once.  On  the  other  hand,  is  it  necc^vsary 
for  Kallima,  the  simulator  of  dead  leaves,  to  go  so  far  as  it  has 
in  its  modification?  Such  minute  points  of  detail  are  there 
as  wdll  never  be  noted  by  bird  or  lizard.  The  simple  necessity 
is  the  effect  of  a  dead  leaf;  that  is  all.  KalUtna  certainly  does 
that  and  more.  Kallima  goes  too  far  and  proves  too  much. 
And  there  are  other  cases  like  it.  Natural  selection  alone  coukl 
never  carry  the  simulation  past  the  point  of  advantage. 

But  whatever  other  factors  or  agents  have  })layed  a  part  in 
bringing  about  this  specialization  of  color  and  j^atttTU,  exem- 
plified by  animals  showing  protective  resemblances,  warning 
colors,  terrifying  manners,  and  mimicry,  natirr;  1  selection  liiuj 
undoubtedly  been  the  chief  factor,  and  the  basis  of  utility 
the  chief  foundation,  for  the  development  of  the  specialized 
conditions. 


CHAPTER  XX 
REFLEXES,    INSTINCT,   AND    REASON 

We  live  in  a  world  which  is  full  of  misery  and  ignorance,,  and  the 
plain  duty  of  each  and  all  of  us  is  to  try  to  make  the  little  corner  he  can 
influence  somewhat  less  miserable  and  somewhat  less  ignorant  than  it 
was  before  he  entered  it.  To  do  this  eiTectuaily  it  is  necessary  to  be 
fully  possessed  of  two  beliefs — the  first,  that  the  ordei'  of  nature  is 
a:3?ertainabie  by  our  faculties  to  an  extent  which  is  practically  un- 
limited; the  second,  that  our  volition  counts  for  something  as  a  condi- 
tion of  the  course  of  events. 

Each  of  these  beliefs  can  be  verified  experimentally  as  often  as  we 
Mke  to  try.  Each,  therefore,  stands  upon  the  strongest  foundation  upon 
which  any  belief  can  rest,  and  forms  one  of  our  highest  truths.  If  we 
find  that  the  ascertainment  of  the  order  of  nature  is  facilitated  by  using 
one  terminology  or  one  set  of  symbols  rather  than  another,  it  is  our 
clear  duty  to  use  the  former;  and  no  harm  can  accrue  so  long  as  we 
bear  in  mind  that  w^e  are  dealing  merely  with  terms  and  symbols. — 
Huxley. 

All  animals  of  whatever  degree  of  organization  show  in 
life  the  quality  of  irritabilit}^  or  response  to  external  stimulus. 
Contact  with  external  things  produces  some  effect  on  each  of 
them,  and  this  elTect  seems  to  be  something  more  than  the 
mere  mechanical  effect  on  the  matter  of  which  the  animal  is 
composed.  In  the  one-celled  animals,  the  functions  of  response 
to  external  stimulus  are  not  localized.  They  are  the  property 
of  any  part  of  the  protoplasm  of  the  body.  Just  as  breathing 
or  digestion  is  a  function  of  the  wdiole  cell,  so  are  sensation  and 
response  in  action.  In  the  higher  or  many-celled  animals 
each  of  these  functions  is  specialized  and  localized.  A  certain 
set  of  cells  is  set  apart  for  each  function,  and  each  organ  or 
series  of  cells  is  released  from  all  functions  save  its  own. 

42G 


REFLEXES,   IXSTIXCT,   AND   REASON  427 

In  tlie  more  liiglily  organized  animals  certain  colls  from  the 
primitive  external  layer  or  ectol)last  of  tlie  omhryo  are  early 
set  apart  to  record  the  relations  of  the  creature  to  its  envircn- 
ment.  These  cells  are  highly  s])ecializ(Hl,  and  while  some  of 
them  are  highly  sensitive,  others  are  adapted  for  carrying 
c:  transmitting  the  stimuli  received  by  the  sensitive  cells,  and 
still  others  have  tiie  function  of  receiving  sense  impressions  and 
of  translating  them  into  impulses  of  motion.  The  nerve  cells 
are  receivers  of  impressions.  These  are  gathered  together  in 
nerve  masses  or  ganglia,  the  largest  of  these  being  known  as 
the  brain,  the  ganglia  in  general  being  known  as  nerve  centers. 
The  nerves  are  of  two  classes.  The  one  class,  called  sensory 
nerves,  extends  from  the  skin  or  other  organ  of  sensation  to 
the  nerve  center.  The  nerves  of  the  oilier  class,  motor  nerves, 
carry  impulses  to  motion. 

The  brain  or  other  nerve  center  sits  in  darkness  surroimded 
by  protecting  tissues  or  a  protecting  ])ox  of  bone.  To  this  bndn, 
nerve  center,  or  sensorium  come  the  nerves  fom  ill  j)a:*tr>  of 
the  body  that  have  sensation — the  external  skin  as  well  as  the 
special  organs  of  sight,  hearing,  taste,  smell.  With  these  come 
nerves  bearing  sensations  of  pain,  temperature,  muscular  effort  — 
all  kinds  of  sensation  which  the  brain  can  receive.  These  nerves 
are  the  sole  sources  of  knowledge  to  any  animal  o/ganism. 
Whatever  idea  its  brain  may  contain  must  be  built  up  through 
these  nerve  impressions.  The  aggregate  of  these  impressions 
constitutes  the  world  as  the  organism  knows  it.  All  sensation 
is  related  to  action.  If  an  organism  is  not  to  act,  it  cannot 
feel,  and  the  intensity  of  its  feeling  is  related  to  its  power  to  act. 

These  impressions  brought  to  the  brain  by  the  sensory 
nerves  represent  in  some  degree  the  facts  in  the  animal's  en- 
vironment. They  teach  something  as  to  its  food  or  its  safety. 
The  power  of  locomotion  is  characteristic  of  animals.  If  they 
move,  their  actions  must  dei)(Mid  on  the  indications  carrieil  to 
the  nerve  center  from  the  outside;  if  they  feed  on  living  orga.i- 
isms,  they  must  seek  their  food;  if,  as  in  many  cases,  other 
hving  organisms  ivrey  on  them,  tl.cy  must  bestir  themselves 
to  escape.  Tlie  im])ulsr  of  hunger  on  tlie  one  hand  and  of  fear 
on  the  other  are  elemental.  The  sensorium  receives  an  im- 
pression that  f(>>d  exists  in  r.  certain  direction.  At  once  an 
impulse  to  motion  is  .sent  out  from  it  to  the  muscle  neces^sary 
t:;)  move  the  body  in  that  direction.     In  the  higher  animals 


428 


EVOLUTION  AND  ANIMAL  LIFE 


these  movements  are  usually  more  rapid  and  more  exact  than 
with  the  lower  forms.  This  is  because  the  organs  of  sense 
and  action^  the  sense  cells,  nerve  fibers,  and  muscles  are  all 
highly  specialized.  In  the  starfish  sensation  is  slight,  nervous 
communication  slow,  and  the  muscular  response  sluggish,  but 

the    method    is   apparently   the 
same. 

But  in  recent  years  many 
biologists  have  come  to  believe 
that  much  of  the  behavior  of 
the  simplest  animals,  and  some 
of  the  actions  of  the  higher, 
are  controlled  in  a  more  rigidly 
mechanical  way  than  the  above 
statements  suggest;  that,  in  a 
word,  much  of  the  action,  and 
apparent  instinctive  or  intelli- 
gent response  of  animals  to  ex- 
ternal conditions,  is  an  immedi- 
ate physicochemical  rather  than 
vital  phenomenon;  that  the 
animal  body  in  its  relation  to 
the  external  world  is  much 
more  like  a  passive,  senseless, 
although  very  complex,  ma- 
chine, stimulated  and  controlled 
by  external  factors  and  con- 
ditions, than  like  the  percipient, 
determining,  purposeful  creature 


Fig.  264. — Diagram  showing  how  the 
Protozoan,  Oxi/tricha  fallax,  reacts  to 
cold;  slide  is  heated  at  upper  end  and 
an  Oryiricha  beginning  at  1  continues 
to  react  by  turning  a  little  to  right 
and  backing  and  advancing  and  re- 
peatedly turning  a  little  to  right  and 
backing  and  advancing  until  posi- 
tion 14  is  reached.    (After  Jennings.)    that  our  usual  couccption  of  the 

organism  makes  it  out  to  be. 

Clever  experimenters,  as  Loeb,  Lucas,  Radl,  Bethe,  Uexkull, 
and  numerous  others,  believe  themselves  justified  in  explaining 
a  host  of  the  simpler  actions  or  modes  of  behavior  of  animals, 
on  a  thoroughly  mechanical  basis,  as  rigorous,  inevitable 
reactions  to  the  influence  or  stimulus  of  light,  heat,  contact, 
gravity,  galvanism,  etc.  Phototropism,  stereotropism,  geo- 
tropism,  etc.,  are  the  names  given  to  these  phenomena  of  re- 
sponse by  action  and  behavior  to  stimuli  of  light,  contact,  and 
gravity  respectively. 

Some  of  these  biologists  are  ready  to  carry  their  giving  up 


REFLEXES,   INSTINCT,   AND   REASON  429 

of  otlier  tlian  mechaniciil  behavior  amon^  aniiiKils  to  great 
lengtlis.  Loel)  introduce.s  a  pajxT  written  in  isiuj  on  instinct 
and  will  in  animals  as  follows: 

*'In  the  biolo«:;i('al  literature  one  still  fiiuls  authors  wlio  treat  the 
'  instinct '  or  the  '  will '  of  animals  as  a  circumstance  wliich  (let<Tniines 
motions,  so  that  the  scientist  who  enters  the  region  of  animated  nature 
encounters  an  entirely  new  category  of  causes,  such  as  are  said  contin- 
ually to  produce  before  our  eyes  great  effects,  without  it  Ix'ing  possible 
for  an  engineer  ever  to  make  use  of  these  causes  in  the  jthysi<Hl  world. 
'  Instinct'  and  '  will'  in  animals,  as  causes  whicli  determine  movements, 
stand  upon  the  same  j^lane  as  the  suj)ernatural  jjowers  of  theologians, 
which  are  also  said  to  determine  motions,  but  uj)on  which  an  engineer 
could  not  well  rely. 

"My  investigations  on  the  heii()lro!)ism  of  animals  IcmI  me  to 
analyze  in  a  few  cases  the  conditions  which  determine  the  ai>parently 
accidental  direction  of  animal  movements  which,  according  to  tradi- 
tional notions,  are  called  voluntary  or  instinctive.  Wherever  I  have 
thus  far  investigated  the  cause  of  such  'voluntary'  or  'instinctive' 
movements  in  animals,  I  have  without  excei)tion  discovered  such 
circumstances  at  work  as  are  known  in  inanimate  nature  as  determi- 
nate movements.  By  the  help  of  these  causes  it  is  possible  to  control 
the  'voluntary'  movements  of  a  living  animal  just  as  securely  and 
unequivocally  as  the  engineer  has  been  able  to  control  the  movenient.s 
in  inanimate  nature.  What  has  been  taken  for  the  effect  of  'will'  or 
'instinct'  is  in  reality  the  effect  of  light,  of  gravity,  of  friction,  of 
chemical  forces,  etc." 

But  Jennings,  a  ver}^  careful  and  industrious  student  of  the 
behavior  of  the  protozoa,  whose  studies  have  been  j)erhaps  more 
detailed  and  prolonged  than  those  of  any  other  investigator  cf 
the  same  subject,  closes  a  fascinating  volume  on  his  work  wi.  . 
the  following  jiaragraph: 

"The  present  paper  may  be  considered  as  the  summ.ng  up  of  the 
general  resuhs  of  several  years'  work  by  the  author  on  the  Ix'havior  of 
the  lowest  organisms.  This  work  has  shown  that  in  thes<'  creatures  the 
behavior  is  not  as  a  rule  on  the  troi»ism  plan— a  set,  force<l  metluxi  of 
reacting  to  each  i)articular  agent— but  takes  place  in  a  nuich  more 
flexil)le,  less  directly  machinelike  way,  by  the  method  of  trial  and 
error.     This  method   involves   many   of   the   fundamental   «|uaHlie8 


430 


EVOLUTION   AND   ANIMAL   LIFE 


which  we  find  in  tlie  beha^dor  of  higher  animals,  yet  with  the  simplest 
possible  basis  in  ways  of  action;  a  great  portion  of  the  behavior  con- 
sisting often  of  but  one  or  two  definite  movements,  movements  that  are 
stereotyped  in  their  relation  to  the  environment.  This  method  leads 
upward,  offering  at  every  point  opportunity  for  development,  and 
showing  even  in  the  unicellular  organisms  what  must  be  considered  the 

beginnings  of  intelligence  and  of  many 
other  qualities  found  in  liigher  animals. 
Tropic  action  doubtless  occurs,  but  the 
main  basis  of  behavior  is  in  these  or- 
ganisms the  method  of  trial  and  error." 


Fig.  265. — Diagram  showing  how 
the  motile  Protozoan,  Stcntor, 
reacts  to  light:  A  circular  space 
half  in  light  and  half  in  dark; 
the  animalcules  collect  in  dark 
area;  1,  2,  and  3  shovr  the 
reaction  of  a  specimen  which 
came  to  the  light  line.  (After 
Jennings.) 


Different  one-celled  animals  show 
differences  in  method  or  degree  of 
response  to  external  influences. 
Most  protozoa  wall  discard  grains 
of  sand,  crystals  of  acid,  or  other 
indigestible  objects.  Such  peculi- 
arities of  different  forms  of  life 
constitute  the  basis  of  instinct. 

Instinct  is  automatic  obedience 
to  the  demands  of  external  condi- 
tions. As  these  conditions  vary 
mth  each  kind  of  animal,  so  must 
the  demand  vary,  and  from  this  arises  the  great  variety  actu- 
ally seen  in  the  instincts  of  different  animals.  As  the  de- 
mands of  life  become  complex,  so  may  the  instincts  become  so. 
The  greater  the  stress  of  environment,  the  more  perfect  the 
automatism,  for  impulses  to  safe  action  are  necessarily  adequate 
to  the  duty  they  have  to  perform.  If  the  instinct  were  inade- 
quate, the  species  ^vould  have  become  extinct.  The  fact  that 
its  individuals  persist  shows  that  they  are  provided  \^dth  the 
instincts  necessary  to  that  end.  Instinct  differs  from  other 
allied  forms  of  response  to  external  conditions  in  being  hereditar}^ 
and  continuous  from  generation  to  generation,  and  in  being 
common  to  the  species  and  not  characteristic  of  the  individual. 
This  sufficiently  distinguishes  it  from  reason,  but  the  line  be- 
tween instinct  and  reason  and  various  forms  of  reflex  action 
cannot  be  sharply  drawn. 

Some  WTiters   regard   instincts  as  "inherited  habit,"  while 
others,  with  apparent  justice,  doubt  if  mere  habits  or  voluntary 


REFLEXES,   INSTINCT,  AND   REASON 


431 


actions  repeated  till  they  become  a  ".-irnii.i  luu uru"  ever  leave 
a  trace  upon  heredity.  Such  investigators  re«(ard  instinct  as 
the  natural  survival  of  those  methods  of  automatic  res|,)onse 
which  were  most  useful  to  the  life  of  the  animal,  the  individuals 
having  less  effective  methods  of  reflex  action  havinj;  perishe<l, 
It^aving  no  posterity. 

An  example  in  point  would  he  the  homing  instinct  of  the 
fur  seal.  When  tlie  arctic  winter  descends  on  its  home  in  the 
Pribilof  Islands  in  Ber- 
ing Sea,  these  animals 
take  to  the  open  ocean, 
many  of  them  swim- 
ming southward  as  far 
as  the  Santa  Barbara 
Islands  in  California, 
more  than  three  thou- 
sand miles  from  home. 
While  on  the  long 
swim  they  never  go 
on  shore;  but  in  the 
spring  they  return  to 
the  northward,  find- 
ing the  little  islands 
hidden  in  the  arctic 
fogs,  often  landing  on 
the    very    spot    from 

which  they  were  dri\en  ])y  the  ice  six  months  before,  and 
their  arrival  timed  from  year  to  year  almost  to  the  same 
day.  The  perfection  of  this  homing  instinct  is  vital  to  their 
life.  If  defective  in  any  individu.,1,  he  would  be  lost  to  tiie 
herd  and  would  leave  no  descendants.  Those  who  return  Ixv 
come  parents  of  the  herd.  As  to  the  others  the  rough  sea 
tells  no  tales.  We  know  that  of  those  that  set  forth  ;«  large 
percentage  never  come  back.  To  those  that  return  the  homing 
instinct  has  proved  adecpiate.  This  nuist  be  so  long  as  the  race 
exists.  The  failure  of  instinct  would  mean  the  extinction  of 
the  species. 

Tlie  instincts  of  animals  may  be  roughly  classified  a,s  to  their 
relation  to  the  individual  into  egoistic  and  altruistic  instincts. 

Egoistic  instincts  are  those  which   concern  chiefly  the  in- 
dividual animal  itself.     To  this  class  belong  tlie  instincts  of 


I'ir..  2G6. — A  "'pointer''  dog  in  the  act  <»f  "|>.>inl- 
inR."  a  siiecialized  instinct  (l'ernii.>'itiun  of  (J.  O. 
Shields,  publisher  of  "  Heereation.'') 


432 


EVOLUTION  AND  ANIMAL  LIFE 


feeding,  those  of  self-defense  and  of  strife,  the  instincts  of  play, 
the  climatic  instincts,  and  environmental  instincts,  those  which 
direct  the  animal's  mode  of  life. 

Altruistic  instincts  are  those  which  relate  to  parenthood 

and  those  which  are  concerned 
with  the  mass  of  individuals  of 
the  same  species.  The  latter 
may  be  called  the  social  instincts. 
In  the  former  class,  with  the  in- 
stincts of  parenthood,  may  be  in- 
cluded the  instincts  of  courtship, 
reproduction,  home-making,  nest- 
building,  and  care  for  the  young. 

The  instincts  of  jeeding  are 
primitively  simple,  growing  com- 
plex through  complex  conditions. 
The  protozoan  absorbs  smaller 
creatures  which  contain  nutri- 
ment. The  sea  anemone  closes 
its  tentacles  over  its  prey.  The 
barnacle  waves  its  feet  to  bring 
edible  creatures  within  its  mouth. 
The  fish  seizes  its  prey  by  direct 
motion.  The  higher  vertebrates 
in  general  do  the  same,  but  the 
conditions  of  life  modify  this 
simple  action  to  a  very  great 
degree. 

In  general,  animals  decide  by 
reflex  actions  what  is  suitable 
food,  and  by  the  same  processes 
they  reject  poisons  or  unsuitable 
sul:)stances.  The  dog  rejects  an 
apple,  while  the  horse  rejects  a 
piece  of  meat.  Either  will  turn 
away  from  the  offered  stone.  Al- 
most all  animals  reject  poisons 
instantly.  Those  that  fail  in  this  regard  in  a  state  of  nature 
die  and  leave  no  descendants.  The  wild  vetches  or  "loco- 
weeds"  of  the  arid  regions  affect  tlie  nerve  centers  of  animals 
and  cause  dizziness  or  death.     The  native  ponies  reject  these 


Fig.  267.— Part  of  branch  of  oak 
tree,  showing  acorns  placed  in 
rcles  in  the  bark  by  the  CaU- 
iornia  woodpecker,  Melanerpes 
formiciiiorus  hairdii.  (From 
photograph  taken  at  Stanford 
University,  CaHfornia.) 


REFLEXES,   IXSTIX(T,   AND   UEASOX  433 

instinctively.  Tliis  may  be  because  all  ponies  which  have  not 
this  reflex  dislike  have  been  destroyed.  The  imported  horse 
lias  no  sucli  instinct  and  is  poisoned.  NCry  few  animals  will 
eat  any  poisonous  object  with  wiiich  their  instincts  are  familiar. 
unless  it  be  concealed  from  smeU  and  taste. 

In  some  cases,  very  elaborate  instincts  arise  in  connection 
with  feeding  habits.  In  the  case  of  the  California  wfM)dpecker.s 
(Melanerpcs  jormicivorus  bainlii)  a  large  number  together  select 
a  live-oak  tree  for  their  operations.  Tliey  first  bor(»  its  bark 
full  of  lioles,  each  large  enough  to  iiold  im  acorn.  Then  into 
each  hole  an  acorn  is  thrust  (Figs.  267  and  :l()S).  Only  one  tree 
in  several  square  miles  may  be  sele-jted,  and  when  their  work  i.s 
finished  all  those  interested  go  aij-out  tiieir  business  elsewhere. 
At  irregular  intervals  a  dozen  or  so  come  b\'.ck  with  much 
clamorous  discussion  to  look  at  the  tree.  Wiien  {\\o  right  time 
comes,  tliey  all  return,  open  the  acorns  one  by  one,  tlevouring 
apparently  the  substance  of  the  nut,  and  probably  also  the 
grubs  of  beetles  which  have  develoi)ed  within.  W'iien  the  nuts 
are  ripe,  again  they  return  to  the  same  tree  and  the  same 
process  is  repeated.  In  the  tree  figured  this  has  been  noticed 
each  year  since  1891. 

The  instinct  of  selj-defense  is  even  more  varied  in  its  mani- 
festations. It  may  show  itself  either  in  the  imj)ulse  to  make 
war  on  an  intruder  or  in  an  impulse  to  flee  from  its  enemies. 
Among  the  flesh-eating  mammids  and  birds  fierceness  of  de- 
meanor serves  both  for  the  securing  of  food  and  for  protection 
against  enemies.  The  stealthy  movements  of  the  lion,  the 
skulking  habits  of  the  wolf,  the  sly  selfishness  of  the  fox,  the 
l)lundcring  good-natured  power  of  the  l)ear,  the  greedines.s  of 
the  hyena,  are  all  proverbial,  and  similar  traits  in  the  eagle. 
owl,  hawk,  and  vulture  are  scarcely  less  matters  of  conuntui 
observation. 

Herbivorous  animals,  as  a  rule,  make  little  direct  resistance 
to  their  enemies,  depending  rather  on  swiftness  of  foot,  or  in 
some  cases  on  simple  insignificance.  To  the  latter  '-ause  thr 
abundance  of  mice  and  mouselike  rodents  may  be  attribute*!. 
for  all  arc  the  prey  of  the  carnivorous  beasts  and  birds,  and 
of  snakes. 

Even  young  animals  of  any  species  show  great  fear  of  their 
hereditary  enemies.  The  nestlings  in  a  nest  of  the  American 
bittern  when  one  week  old  sh.owcl  no  fear  of  man,  but  when 


434 


EVOLUTION   AND   ANIMAL   LIFE 


two  weeks  old  this  fear  was  A^ery  manifest.  Young  mocking 
birds  will  go  into  spasms  at  the  sight  of  an  owl  or  a  cat,  while 
they  pay  little  attention  to  a  dog  or  a  hen.     Monkeys  that  have 


r~w 


Fig.  268. — Section  of  bark  of  the  live-oak  tree,  with  acorns  placed  on  it  by  the  California 
woodpecker,  Melanerpes  formicivorus  bairdii.  (From  photograph  taken  at  Stanford 
University,  California.) 


never  seen  a  snake  show  almost  hj^sterical  fear  at  first  sight  of 
one,  and  the  same  kind  of  feeling  is  common  to  most  men.  A 
monkey  was  allowed  to  open  a  paper  bag  which  contained  a, 


REFLEXES,   LNSTIXCl,   AM)   UlOASuN 


435 


live  snake.  He  was  staggtMcd  hy  tlic  si^rht,  Init  aft<T  a  while 
he  went  back  and  looked  ajL!:ain,  to  rejjcat  the  oxi)ericnc('.  J-^ich 
wild  animal  has  its  special  instinct  of  resistance  or  method  of 
keeping  off  its  enemies.  T\h)  stamping  of  a  sheep,  the  kicking 
of  a  horse,  the  running;  in  a  circle  of  a  hare,  and  the  skulking 
in  a  circle  of  some  foxes,  are  exami)l('s  of  this  sort  of  instinct. 


Fig.  209. — Ne.«*tlings  of  the  -Amerrcan  bittern,  two  of  a  brood  of  four  birds  one  week  oUI, 
at  which  age  they  showed  no  fear  of  man.  (Photoiifraph  by  K.  N.  Tn)>or,  .MiTidian, 
N,  Y.,  May  31,  1898.     Permission  of  Macmillaii  Co..  pubh.sher.x  of  "Bird  l.<>tx\") 

The  play  instinct  is  developed  in  numerous  animals.  To 
this  class  belong  the  wrestlings  and  mimic  fights  of  young 
dogs,  bear  ciil)S,  seal  pups,  and  young  beasts  generally.  (  ats 
and  kittens  play  with  mice.  Stjuirrels  j)lay  in  the  trees.  Per- 
haps it  is  the  play  imjiulse  tiuit  leads  the  shrike  or  butcher  bird 
to  impale  small  l)irds  and  l)eetles  on  tlie  thorns  about  its  nest, 
a  gliastly  kind  of  ornament  tliat  seems  to  confer  satisfaction 
on  the  bird  itself.  The  talking  of  tlie  parrots  and  their  imita- 
tions of  the  sounds  they  hriiv  seem  to  be  of  the  nature  of  |)lay. 
The  greater  their  superfluous  (»nergy  the  more  they  will  talk. 
Much  of  the  singing  of  birds,  and  the  crying,  calling,  ami  howling 


436 


EVOLUTION  AND  ANIMAL  LIFE 


of  other  animals,  are  mere  play,  although  singing  primarily 
belongs  to  the  period  of  reproduction,  and  other  calls  and  cries 
result  from  social  instincts  or  from  the  instinct  to  care  for  the 
young. 

Climatic  instincts  are  those  which  arise  from  the  change  of 


Fig.  270. — Nestlings  of  American  bittern.  P'our  birds,  of  which  two  are  shown  in  Fig. 
269,  two  weeks  old,  at  which  age  they  showed  marked  fear  of  man.  (Photograph 
by  E.  N.  Tabor,  Meridian,  N.  Y.,  June  8,  1898.  Permission  of  Macmillan  Co., 
pubUshers  of  "Bird  Lore.") 

the  seasons.  When  the  wdnter  comes  the  fur  seal  takes  its 
long  swim  to  the  southward;  the  "^dld  geese  range  themselves 
in  wedge-shaped  flocks  and  fly  high  and  far,  calling  loudh^  as 
they  go;  the  bobolinks  straggle  away  one  at  a  time,  flying 
mostly  in  the  night,  and  most  of  the  smaller  birds  in  cold 
countries  move  away  toward  the  tropics.  All  these  movements 
spring  from  the  migratory  instinct.  Another  climatic  instinct 
leads  the  bear  to  hide  in  a  cave  or  hollow  tree,  where  he  sleeps 


REFLEXES,   JXSTJXCT,   AND   lU:.\.SOX 


4.37 


or  hibernates  till  sprin-.  In  sonic  cases  the  climatic  instinct 
merges  in  the  honiino;  instinct  an.l  the  instinct  of  reproduction. 
V\h(Mi   the   l,u-(ls  move   nortli   hi   the  sprii.fr  thev  Mn^^   mate 


and  build  their  nests.     Tlie  fur  seal  jrnes  home  to  rear  its  yountr. 
The  bear  exchanges  its  bed  for  its  lair,  and  its  first  ht  -> 

after  waking -is  to  make  ready  to  rear  its  young. 
?9 


438 


EVOLUTION  AND  ANIMAL  LIFE 


Environmental  insiincts  concern  the  creature's  mode  of  life. 
Such  are  the  burrowing  instincts  of  certain  rodents,  the  wood- 
chucks,  gophers,  and  tlie  hke.  To  enumerate  the  chief  phases 
of  such  instincts  would  be  difficult,  for  as  all  the  animals  are 
related  to  their  environment,  this  relation  must  show  itself  in 
characteristic  instincts. 

The  instincts  of  courtship  relate  chiefl}^  to  the  male,  the  female 
being  more  or  less  passive.    Among  the  birds  the  male  in  spring 

is  in  very  many  species 
provided  with  an 
ornamental  plumage 
which  he  sheds  when 
the  breeding  season 
is  over.  The  scarlet, 
crimson,  orange,  blue, 
black,  and  lustrous 
colors  of  birds  are 
commonl}^  seen  only 
on  the  males  in  the 
breeding  season,  the 
young  males  and 
the  old  males  in  the 
fall  having  the  plain 
brown  gray  or  streaky 
colors  of  the  female. 
Among  the  singing 
birds  it  is  chiefly  the 
T.     ^,^    TT         .  ,,.,,,,,      male  that   sings,  and 

i^iG.  272! — Horns  of  two  male  deer  interlocked  while  '  .  j       i 

fighting.     (Permission  of  G.  O.  Shields,  publisher       hlS    VOlCe    and    the    m- 

of  "Recreation.")  stinct    to    use   it    are 

commonly  lost  in 
great  degree  when  the  young  are  hatched  in  the  nest.  Among 
certain  fishes  the  males  are "  especially  brilliantly  colored  in  the 
breeding  time,  but  there  is  little  evidence  of  any  personal  at- 
tempts to  display  these  colors  before  the  females. 

Among  polygamous  mammals  the  male  is  usually  much 
larger  than  the  female,  and  his  courtship  is  often  a  struggle 
with  other  males  for  the  possession  of  the  female.  Among 
the  deer  the  male,  armed  with  great  horns,  fight  to  the  death 
for  the  possession  of  the  female  or  for  the  mastery  of  the  herd. 
The  fur  seal  has  on  an  average  a  family  of  about  thirty-two 


REFLEXES,    IXSTLMT,   AM)   lU:.\SON  439 

feinakvs,  and  for  the  control  of  his  harcni  others  are  ready  at  all 
times  to  dispute  tlie  possession.  But  with  niono^ainous  animals 
like  the  true  or  hair  seal  or  fox,  where  a  male  mates  with  a  single 
female,  there 'is  no  such  diserepancv  in  size  and  strength,  and 
the  warlike  force  of  the  male  is  spent  on  outside  enemies,  not 
on  his  ow^n  si)ecies. 

The  movements  of  many  mijrratory  animals  are  mainly  con- 
trolle:!  by  the  impulse  to  reproduce.     Some  pelagic  '  >- 

pecially  Hying  fishes  and  fishes  allied  to  the  mackerel,  swim 
long  distances  to  a  region  favorable  for  a  disj)osiiion  of  Hpawn. 
Some  spectes  are  known  only  in  the  waters  they  mak**  their 
breeding  homes,  the  individuals  being  scattered  th»-ough  the 
wide  seas  at  other  times.  -Many  fresh-water  fishes,  as  trout, 
suckers,  etc.,  forsake  the  large  streams  in  the  spring,  jiscending 
the  small  brooks  where  they  can  rear  their  young  in  greater 
safety.  Still  others,  known  as  anadromous  fish(»s,  feeii  and 
mature  in  the  sea,  but  ascend  the  rivers  as  the  impulse  of  re- 
production grows  strong.  Among  such  s}>ecies  are  the  salmon, 
shad,  alewife,  sturgeon,  and  sirij)ed  bass  in  American  waters. 
Tlie  most  noteworthy  case  of  the  anadromous  instinct  is  found 
in  the  king  salmon  or  quinnat  of  the  Pacific  coast.  This  gn'at 
fish  spawns  in  November.  In  the  Columbia  River  it  begins 
running  in  March  and  April,  spending  the  whole  sunimer  in 
the  ascent  of  the  river  witliout  feeding.  \\y  autumn  the  in- 
dividuals are  greatly  changed  in  ai)|)earance,  discolore(l,  worn, 
and  distorted.  On  reaching  the  spawning  beds,  some  of  them 
a  thousand  miles  from  the  sea,  the  female  deposits  her  eggs  in 
the  gravel  ©f  some  shallow  brook.  After  they  are  fertilizcni 
both  male  and  female  tlrift  tail  foremost  and  hel|>h»ss  <lown  the 
streini,  none  of  them  ever  surviving  to  reach  the  sea.  The  ."^iimo 
habits  are  found  in  other  species  of  salmon  of  the  l*acific,  but 
in  most  cases  the  individuals  of  other  species  do  not  start  so 
early  or  run  so  far.  A  few  species  of  fishes,  as  the  eel,  reverse 
this  order,  feeding  in  the  rivers  and  brackish  creeks,  dropping 
down  to  the  sea  to  si)awn. 

The  migration  of  l)irds  has  relation  to  reproduction  as  well 
as  to  changes  of  weather.  As  soon  as  they  reach  their  summer 
homes,  courtship,  mating,  nest-building,  and  the  care  of  the 
young  occupy  the  attention  of  every  species. 

In  the  animal  kingdom  one  of  the  great  factors  in  develo|)- 
jncnt  k-a?'  l^f'^n  the  care  oj  the  yoiuvj.    This  feat  urv*  is  a  prominent 


440 


EVOLUTION    AND   ANIMAL   LIFE 


RKFLKXKS.    INSTINCT,   AM>   HK.MiOS 


4U 


one  in  the  .specializatirwi  of  Ijinls  ami  mainuiai.-,.  W  i.en  tl»e 
young  are  cared  for  the  jxTcenta^^e  of  lo.s.s  in  llu-  str  '  for 
life  is  greatly  n'(hice(l,  the  niinilM-r  of  ])irths  iieeeHSiirv  lo  ihc 


Fivi.  274.— Nebt  and  fK^s  <»f  tlu'  Uiifiis  huintniti(;Mr<l.  7V. 

J.  O.  SiiydiT,  Stanford  I'mvcr-^' v     f  ,,...- 


l'li»(<itf  r»i'U  hy 


iTiaintenanee  of  tlie  species  is  much  less,  and  the  op|>ort unities 
for  specialization  in  other  relations  of  life  are  nnich  proator. 
In  these  regards,  the  nest-huilding  and  honio-niakinp  aninv^^*^ 
have  tlie  advantage  over  those  tliat  have  not  those  iiiiJtinc;.-. 


442 


EVOLUTION  AND  ANIMAL  LIFE 


The  animals  that  mate  for  life  have  the  advantage  over  polyg-^ 
amous  animals,  and  those  whose  social  or  mating  habits  give 


Fn..  27'j. — Ahricial  nestlings  of  the  blue  jay,  Cyanocittu  aistata. 

rise  to  a  division  of  labor  over  those  with  instincts  less  highly 
specialized. 

Wlien  we  study  instincts  of  animals  with  care  and  in  detail, 
we  find  that  their  regularity  is  much  less  than  has  been  sup- 
posed.    There  is  as  much  variation  in  regard  to  instinct  among 


REFLEXES,    LXSTINCT,   AM)   REASON 


44:^ 


individuals  as  there  is  with  regard  to  other  characters  of  the 
species.  Some  power  of  choice  is  fouiul  in  almost  every  o|KTa- 
tion  c:  instinct.  Even  tlie  most  macliinelike  ii».stinct  shows 
some  degree  of  a(hiptal)iHt y  to  new  conditions.  On  the  otiier 
hand,  in  no  animal  chx's  reason  show  entire  frcMMloin  from 
automatism  .ir  reflex  action.  "The  fundr.iiH-iual  identity  of 
instinct  witli  intelli<>;ence/'  says  an  ahle  in\  itor,  "is  sli'own 

in  their  dependence  upon  the  s.imc  stiuctiral  mechani.'^m  (the 
brain  and  nerves),  and  in  their  rcsjjonsive  adaptai)iiity." 


r 


iWl^' 


-^:^<j:^L., 


ll...    _I(t».       A   wild  illU'k.     Xiilli'ii.  I;miil\  ;     lu.ilc     fcnnlr     :»ri.l  lira  ctH-ml   v.iwii!! 


Reason  or  intellect,  as  distin.Lniished  from  instinct,  is  the 
choice,  more  or  l(»ss  conscious,  amonix  responses  to  external 
impressions.     Its  basis,  like  that  of  instiiict.  is  in  reflex  action. 
Its    operations,    often    jepeated,    become'  similarly    reflex    by 
repetition,  and  are  known  as  habit.     A  hal>it   is  a  voluntary 
action  repeated  until  it  becomes  reflex.     It  is  t'»rnti;'.l!v  likr 
instinct  in  all  its  manifestations.     The  only  evident  <• 
is  in  its  3ri<!;in.     Instinct  is  inherite<l.     Habit  is  the  reac: 
produced  within  the  indi\idual   by  its  own  reiK-atc-ii  acti*-: 
In  the  varied  relations  of  life  the  pure  reflex  action  l)eeom<'s 
inadequate.     The  sensorimn  is  ofl'ere<l  a  choice  of  res|>on 
To  choose  one  and  to  reject  the  othes  is  tlie  function  of  \\\\v\. 
or  reason.      While  its  excessive  development  in  man  ob  -  its 

close  relation  fo  insfiuct.  bofli  sliadc  otT  bv  dctrrecs  into  reflex 


444 


EVOLUTION   AND   ANIMAL   LIFE 


action.  Indeed,  no  sharp  line  can  be  drawn  between  uncon- 
scious and  subconscious  choice  of  reaction  and  ordinary  in- 
tellectual processes. 

Most  animals  have  little  self-consciousness,  and  their  reason- 
ing powers  at  best  are  of  a  low  order;  but  in  kind,  at  least,  the 
powers  are  not  different  from  reason  in  man.     A  horse  reaches 

over  the  fence  to  be 
company  to  another. 
This  is  instinct.  When 
it  lets  down  the  bars 
with  its  teeth,  that 
is  reason.  When  a 
dog  finds  its  way 
home  at  night  by  the 
sense  of  smell,  this 
ma\^  be  instinct ;  when 
he  drags  a  stranger  to 
his  wounded  master, 
that  is  reason.  When 
a  jack  rabbit  leaps 
over  a  bush  to  escape 
a  dog,  or  runs  in  a 
circle  before  a  coyote, 
or  when  it  lies  flat  in 
the  grass  as  a  round 
ball  of  gray,  indistin- 
guishable from  grass, 
this  is  instinct.  But 
the  same  animal  is 
capable  of  reason — 
that  is,  of  a  distinct  choice  among  lines  of  action.  Not  long 
ago  a  rabbit  came  bounding  across  the  university  campus  at 
Palo  Alto.  As  it  passed  a  corner  it  suddenly  faced  two  hunting 
dogs  running  side  by  side  toward  it.  It  had  the  choice  of  turning 
back,  its  first  instinct,  but  a  dangerous  one;  of  leaping  over  the 
dogs,  or  of  lying  flat  on  the  ground.  It  chose  none  of  these,  and 
its  choice  was  instantaneous.  It  ceased  leaping,  ran  low,  and 
went  between  the  dogs  just  as  they  were  in  the  act  of  seizing  it, 
and  the  surprise  of  the  dogs,  as  they  stopped  and  tried  to  hurry 
around,  was  the  same  feeling  that  a  man  would  have  in  like 
circumstances. 


Fig.  277. — Tailor  bird.  Orniihoiomus  sutorius,  and 

nest. 


REFLEXES,    INSTINCT,   AND    1{I:aS()N  J  j.", 

On  tlic  oiH'ii  ])laiiis  of  Merced  County,  Cal.,  the  jack  ral)bit 
is  the  prey  of  the  bald  eagle.  Not  h)ng  since  a  ra))bit  pursued 
by  an  eagle  was  seen  to  run  among  the  cattle.  Leapini^  from 
cow  to  cow,  he  used  these  animals  as  a  shelter  from  the  savage 
bird.  When  the  i)ursuit  was  closer,  the;  rabl>it*  broke  cover 
for  a  barbed-wire  fence.  When  the  eagle  swoojkhI  down  on  it, 
the  rabbit  moved  a  few  inches  to  the  right,  and  the  eagle  could 
not  reach  him  tlirougli  the  fence.  W  hen  the  eagle  came  down 
on  the  other  side,  he  moved  across  to  the  first.  And  this  was 
continued  until  the  eagle  gave  uj)  the  chase.  It  is  instiiu-t 
that  leads  the  eagle  to  swoop  on  the  rabbit.  It  is  instinct  again 
for  the  rabbit  to  run  away,  l^ut  to  run  along  the  line  of  a 
bai bed-wire  fence  demands  some  degree  of  rea.son.  If  theneeil 
to  repeat  it  arose  often  in  the  lifetime  of  a  single  rabbit  it  woul«l 
become  a  habit. 

The  difference  l^etween  intellect  and  instinct  in  lower  animals 
mc\y  be  illustrated  by  the  conduct  of  certain  monkeys  brought 
into  relation  with  new  experiences.  At  one  time  we  had  two 
adult  monkeys,  "Bob"  and  ".locko,"  belonging  to  the  genus 
MacacHS.  Neither  of  these  possessed  the  egg-eating  instinct. 
At  the  same  time  we  had  a  bab}'  monkey,  "  Mono."  of  the  genus 
Cercopitheciis.  Mono  had  never  seen  an  egg.  but  his  inl.e:ited 
impulses  bore  a  direct  relation  to  feeding  on  eggs,  just  lus  the 
heredity  of  Macacus  taught  the  others  how  to  crack  nuts  or 
to  peel  fruit. 

To  each  of  these  monkeys  we  gave  an  egg.  the  first  that  any 
of  them  had  ever  seen.  The  baby  monkey.  Mono,  being  of  an 
egg-eating  race,  devoured  his  egg  by  the  o|)eration  of  instinct 
or  inherited  hal)it.  On  being  given  the  egg  for  the  first  time, 
he  cracked  it  with  his  upper  teeth,  making  a  hole  in  it .  and  sucktnl 
out  all  the  substance.  Then  holding  the  eggshell  uj)  to  th.e 
light  and  seeing  that  there  was  no  longer  anything  in  it.  he 
threw  it  away.  All  this  he  did  mechanically,  automatically, 
and  it  was  just  as  well  done  with  the  first  egg  lie  ever  siiw  as 
with  any  other  he  ate.  All  eggs  since  offered  him  he  has  treateil 
in  the  same  way. 

The  monkey  Jiob  look  the  egg  for  .some  kind  of  nut.  He 
broke  it  against  his  upper  teeth  and  tried  to  i»ull  ofT  tl»e  .^iliell. 
when  the  inside  ran  out  and  fell  on  the  grouiul.  He  looketi  at  it 
for  a  moment  in  bewilderm<'nt .  took  both  hands  and  sc(M)Imm1  up 
the  volk  and  the  sand  with  whifh  it  was  mixcfl  and  swallowoi 


446 


EVOLUTION   AND  ANIMAL  LI¥E 


Fig.  278. — A  monkey,  Cerocopiihecus,  in  a  characteristic  altitude. 


RKFT.KXKS,    IXSTINCT,     \Nh    Hl..\.^ijS  447 

the  whole.  Then  lie  stulTt^l  the  sliell  itself  iiuu  ius  inoiuh. 
This  act  was  not  instinctive,  h  was  tlie  work  of  pure  rea.>i(»n. 
Evidently  his  race  was  not  familiar  with  the  ase  of  e^^s  and  liad 
acquired  no  instincts  re^ardin^^  tlieni.  He  would  do  it  Ix'ticr 
next  time.  Reason  is  an  inellicient  agent  at  first,  a  weak  t<K)l; 
but  when  it  is  trained  it  becomes  an  agent  more  valual>le  antl 
more  powerful  than  any  instinct. 

The  monkey  Jocko  tried  to  eat  the  e^^  ofTered  liim  in  much 
the  same  way  that  l^ob  (\'u\,  but  not  liking  the  taste  lie  threw 
it  away. 

The  confusion  of  higldy  perfected  insiinci  wiiii  inieiieci  i.s 
very  common  in  popular  discussions.  Instinct  grows  weak 
and  less  accurate  in  its  automatic  obedienee  as  the  intellect 
becomes  available  in  its  place.  Intellect  and  instinct  as  well  ls 
all  other  nervous  processes  are  outgrowths  from  the  simple 
reflex  response  to  external  conditions.  Hut  instinct  insures  a 
single  deiinite  response  to  the  corresi)Mnding  stimulus.  The 
intellect  has  a  choice  of  responses.  In  its  lower  stages  it  is 
vacillating  and  ineffective;  but  as  its  development  goes  on  it 
becomes  alert  and  adecjuate  to  the  varied  conditions  of  life. 
It  grows  with  the  need  foi*  iui))r<tvement.  It  will  tlierefore 
become  impossible  for  tlie  c()m[)lexity  of  life  to  outgrow  the 
adequacy  of  man  to  adapt  himself  to  its  conditions. 

Many  animals  currently  ))elieved  to  be  of  high  intelligence 
are  not  so.  The  fur  seal,  for  example,  finds  its  way  back  from 
the  long  swim  of  two  or  three  tliouiand  miles  tlirough  a  foggy 
and  stormy  sea,  and  is  never  too  late  or  too  early  in  arrival. 
The  female  fur  seal  goes  two  hundred  miles  to  her  fetniing 
gi'ounds  in  summer,  leaving  the  ])up  on  the  shore.  After  a 
week  or  two  she  returns  to  fin<l  him  witiiin  a  few  rods  of  the  rocks 
where  she  had  left  him.  Hotli  mother  and  young  know  each 
other  by  call  and  by  odor,  and  neither  is  ever  mistaken  though 
ten  thousand  other  ])ups  and  other  mothers  occupy  the  .>i:ime 
rookery.  But  this  is  m)t  intellig<'nce.  It  is  simply  instinct, 
because  it  has  no  elem(»nt  of  choice  in  it.  ^^'hatever  its  an- 
cestors were  forcecl  to  do  tiie  fur  seal  does  to  |K'rfection.  Its 
instincts  are  jierfect  as  clockwork,  and  the  necessities  of  migra- 
tion must  keej)  them  so.  Hut  if  brought  into  new  ccmditions 
it  is  dazed  and  stupid.  It  cannot  choo.se  when  different  lines 
of  action  are  presented. 

The    Bering  Sea  Commission  of    iMKi  made  an  ex|x-riment 


44S  EVOLUTION  AND  ANIMAL  LIFE 

on  the  possibility  of  separating  the  young  male  fur  seals,  or 
"killables/^  from  the  old  ones  in  the  same  band.  The  method 
was  to  drive  them  through  a  wooden  chute  or  runway  with 
two  valvelike  doors  at  the  end.  These  animals  can  be  driven 
like  sheep,  but  to  sort  them  in  the  way  proposed  proved  im- 
possible. The  most  experienced  males  would  beat  their  noses 
against  a  closed  door,  if  they  had  seen  a  seal  before  them  pass 
through  it.  That  this  door  had  been  shut  and  another  opened 
beside  it  passed  their  comprehension.  They  could  not  choose 
the  new  direction.  In  like  manner  a  male  fur  seal  will  watch 
the  killing  and  skinning  of  his  mates  with  perfect  composure. 
He  will  sniff  at  their  blood  with  languid  curiosity;  so  long  as  it 
is  not  his  own  it  does  not  matter.  That  his  own  blood  may 
flow  out  on  the  ground  in  a  minute  or  two  he  cannot  foresee. 

Reason  arises  from  the  necessity  for  a  choice  among  actions. 
It  may  arise  as  a  clash  among  instincts  which  forces  on  the  animal 
the  necessity  of  choosing.  A  doe,  for  example,  in  a  rich  pasture 
has  the  instinct  to  feed.  It  hears  the  hounds  and  has  the 
instinct  to  flee.  Its  fawn  may  be  with  her  and  it  is  her  instinct 
to  remain  and  protect  it.  This  may  be  done  in  one  of  several 
ways.  In  proportion  as  the  mother  chooses  wisely  w^ill  be  the 
fawn's  chance  of  survival.  Thus  under  difficult  conditions, 
reason  or  choice  among  actions  rises  to  the  aid  of  the  lower 
animals  as  w^ell  as  man. 

The  word  mind  is  popularly  used  in  two  different  senses. 
In  the  biological  sense  mind  is  the  sum  total  of  all  psychic 
changes,  actions,  and  reactions.  Under  the  head  of  ps3^chic 
functions  are  included  all  operations  of  the  nervous  system 
as  well  as  all  functions  of  like  nature  which  may  exist  in  organ- 
isms without  specialized  nerve  fibers  or  nerve  cells.  As  thus 
defined  mind  would  include  all  phenomena  of  irritability,  and 
even  plants  have  the  rudiments  of  it.  The  operations  of  the 
mind  in  this  sense  need  not  be  conscious.  With  the  lower 
animals  almost  all  of  them  are  automatic  and  unconscious. 
With  man  most  of  them  must  be  so.  All  functions  of  the  sen- 
sorium,  irritability,  reflex  action,  instinct,  reason,  volition, 
are  alike  in  essential  nature  though  differing  greatly  in  their 
degree  of  specialization. 

In  another  sense  the  term  mind  is  applied  only  to  con- 
scious reasoning  or  conscious  volition.  In  this  sense  it  is 
mainly  an  attribute  of  man,  the  lower  animals  showing  it  in 


REFLEXES,    INSTINCT.   AND   REASON  MO 

but  sliglit  (Icgroe.  Tlio  discussion  as  to  whether  lower  animals 
have  minds  turns  on  tlie  definition  of  mind,  and  our  answer  to 
it  depends  on  ihe  definition  we  adopt. 

Most  ])hints  arc  sessile  orf^anisms.  Kiuh  is  an  or^anie  eol- 
ony  of  cells,  with  th(^  power  of  motion  in  parts  hut  not  that  of 
locomotion,  'J'he  i)lant  draws  its  nourishment  from  inorganic 
nature — from  air  and  water.  Its  life  is  not  conditioned  on  a 
search  for  food,  nor  on  the  movement  of  the  hody  as  a  whole. 
Yet  the  |)lant  searches  for  food  hy  a  movenjent  of  the  fee<l- 
ing  parts.  In  the  process  of  growth,  as  l)arwin  has  shown, 
the  tips  of  the  branches  and  roots  are  in  constant  motion.  This 
movement  is  a  spiral  s(piirm.  The  movement  of  the  tendrils 
of  the  growing  vine  is  only  an  exaggeration  of  the  same  action. 
The  course  of  the  S([uirming  rootlet  may  be  deflected  from  a 
regular  s})iral  by  the  presence  of  water.  The  moving  branchlets 
will  turn  toward  the  sun.  The  region  of  .sensation  in  the  plant 
and  the  point  of  growth  are  identical  because  this  i,s  the  only 
part  that  needs  to  move.  T\w.  tender  tip  is  the  plant's  l)rain. 
If  locomotion  were  in  question  the  ))lant  would  need  to  Ik* 
differently  constructed.  It  would  demand  the  mechanism  of 
the  animal.  The  nerve,  brain,  and  muscle  of  the  plant  are  all 
represented  by  the  tender  growing  cells  of  the  moving  tijw. 
The  plant  is  touclied  by  moisture  or  sunlight.  It  may  be  said, 
in  somewhat  metajihorical  language,  that  it  "thinks ''of  them, 
and  in  so  doing  the  cells  that  are  touched  and  "think"  are 
turned  tow-ard  the  source  of  the  stinuilus.  The  function  of 
the  brain,  therefore,  in  some  sense  exists  in  the  tree,  but  there 
's  no  need  in  the  tree  for  a  specialized  sensorium. 

The  many-celled  animals  from  the  lowest  to  the  highest, 
•oear  in  their  organization  .some  relation  to  locomotion.  The 
animal  feeds  on  living  creatures  and  these  it  must  i)ursue  if  it 
is  to  thrive.  It  is  not  the  .sensitive  nerve  tij)s  which  are  to 
move;  it  is  the  whole  creature.  By  the  division  of  labor  the 
whole  body  of  the  comj^ound  organism  cannot  be  given  over 
to  sensation.  Hence  the  development  of  .'^en.^e  organs  dif- 
ferent in  character:  one  stimulated  l)y  waves  of  light,  another 
by  waves  of  sound;  one  .sensitive  to  odor,  another  to  taste; 
still  others  to  contact,  temperature,  nuiscular  strain,  and  pain. 
These  sense  organs  nuist  through  their  nerve  fibers  rc|>ort  to 
a  sensorium  which  is  distinct  from  each  of  them.  And  in 
the  process  of  specialization  the  sensorium    itself    is  subdi- 


450  EVOLUTION   AND   ANIMAL   LIFE 

vided  into  higher  and  lower  nerve  centers;  centers  of  con- 
scious thought  and  automatic  transfer  of  impulse  into  motion. 
This  transfer  indicates  the  real  nature  of  all  forms  of  nerve 
action.  All  are  processes  of  transfer  of  sensation  into  move- 
ment. The  sensorium  or  brain  has  no  knowledge  except  such 
as  comes  to  it  from  the  sense  organs  through  the  ingoing  or 
sensory  nerves.  It  has  no  power  to  act  save  by  its  control  of 
the  muscles  through  the  outgoing  or  motor  nerves.  The  mind 
has  no  teacher  save  the  senses;  no  servants  save  the  muscles. 

The  study  of  the  development  of  mind  in  animals  and  men 
gives  no  support  to  the  medieval  idea  that  the  mind  exists  as 
an  entity  apart  from  the  organ  through  which  it  operates. 
This  "  Klavier  theory  '^  of  the  mind,  that  the  ego  resides  in  the 
brain,  playing  upon  the  cells  as  a  musician  upon  the  strings  of 
a  piano,  finds  no  warrant  in  fact.  So  far  as  the  evidence  goes, 
v/e  know  of  no  ego,  except  that  which  arises  from  the  coordina- 
tion of  the  nerve  cells.  All  consciousness  is  "colonial  conscious- 
ness," the  product  of  cooperation.  It  stands  related  to  the 
action  of  individual  cells  much  as  the  content  of  a  poem  with 
the  words  or  letters  composing  it.  Its  existence  is  a  phenomenon 
of  cooperation.  The  "I"  in  man  is  the  expression  of  the  co- 
working  of  the  processes  and  impulses  of  the  brain.  The  brain 
is  made  of  individual  cells,  just  as  England  is  made  of  individual 
men.  To  say  that  England  wills  a  certain  deed,  or  owns  a 
certain  territory,  or  thinks  a  certain  thought  is  no  more  a  figure 
of  speech  than  to  say  that  "I  will,"  "I  own,"  or  "I  think." 
The  "England"  is  the  expression  of  union  of  the  individual 
wills  and  thoughts  and  ownerships  of  Englishmen.  Similarly, 
my  "ego"  is  the  aggregate  resulting  from  coordination  of  the 
elements  that  make  up  my  body. 

That  what  we  really  know  of  human  personality  tells  the 
whole  story  of  it  no  one  should  maintain.  It  is  well,  how^ever, 
not  to  ascribe  to  it  entities  and  qualities  of  which  we  know 
nothing. 


CITAl^T.R    XX r 
MAN'S   PLAC€   IN    NATURE 

A  sacred  kinsliip   I   would  not   forojjo 

Binds  me  to  all   tliat    hrcathes:  tiirou-rh  «iidl.-s^  <tr\\ 

The  calm  ajid  deathless  di«^iiity  of  life 

Unites  each  blccdinj:;  victim  to  its  foe. 

■  •  •  •  . 

I  am  the  child  of  earth  ami  air  and  S4«a. 

My  lullaby  by  hoarse  Silurian  storms 

Was  chanted,  and  throup:h  endless  changing  f«)nn8 

Of  tree  and  bird  and  l)east  unceasin<;ly 

The  toiling  ages  wrought   to  fashion  me. 

Lo!  these  large  ancestors  have  left  a  breath 
Of  their  great  souls  in  mine,  defying  death 
And  change.     I  grow  and  blossom  as  the  tree, 
And  ever  feel  deep-delving  earthy  roots 
Binding  me  daily  to  the  common  clay: 
Yet  with  its  airy  impulse  ujtward  shoots 
My  soul  into  the  realms  of  light   and  day. 
And  thou,^  O  sea,  stern  mother  of  my  soul, 
Thy  tempests  ring  in  me,  thy  billows  roll! 

—  H.IAI..MAK    lljOHTH    I*<1YF.SF:\. 

IMan  betrays  his  relation  to  what  is  Im-Iow  him,  thick-skulled, 
small-brained,  fishy,  <|uadrumanous  (|uadru|>e(i.  ill-disguis<Ml,  hardly 
escaped  into  bipeil,  and  has  j)aid  for  the  new  p(nvers  by  the  lo.ss  of  some 
of  the  old  ones.  Hut  the  lightning  which  explodes  and  fashions  planet.x, 
maker  of  ])lanets  and  suns,  is  in  hifu.  ( )n  the  one  si«le  elemental  «)nler, 
sandstone  and  granite,  rock  ledges,  peat  bog.  forest,  sen.  and  shon». 
On  the  other  part,  thought  and  the  spirit  whicli  comp(>.««'s  and  deeoin- 

4ol 


452 


EVOLUTION  AND  ANIMAL  LlFti 


poses  nature.  Here  they  are  side  by  side,  god  and  devil,  mind  and 
matter,  king  and  conspirator,  belt  and  spasm  riding  peacefully  to- 
gether in  the  eye  and  brain  of  every  man. — Emerson. 

The  ape  is  this  rough  draft  of  man.  Mankind  have  their  gradations 
as  well  as  the  other  productions  of  the  globe.  There  are  a  prodigious 
number  of  continued  links  between  the  most  perfect  man  and  the 
ape. — John  Wesley. 

One  of  the  most  important  results  of  Darwin's  studies  of 
the  origin  of  species  has  been  the  complete  change  in  the  philo- 
sophical conception  of  man.  We  no  longer  think  of  the  human 
race  as  a  completed  entity  in  the  midst  of  Nature,  but  apart 


Fig.  279. — Skulls  of  man  and  the  orang-utan:  1,  skull  of  a  seven-year-old  German 
child;  2,  skull  of  an  Australian  from  Murray  Kiver;  3,  skull  of  young  orang-utan; 
4,  skull  of  a  grown  orang-utan.      (After  Wiedersheim;  one-sixth  natural  size.) 


from  it,  with  a  different  origin,  a  different  motive,  a  different 
destiny.  Man  is  like  the  other  species,  an  inhabitant  of  the  earth , 
a  product  of  the  laws  of  life;  his  characters  are  phases  in  the 
long  process  of  change  and  adaptation  to  which  all  organisms 
are  subject.  From  the  point  of  view  of  zoology,  the  human 
race  is  a  group  of  closely  allied  species,  or  subspecies,  undoubte^l- 


MANS   PLACE   IN    aaIURE 


4:>.; 


>l)|iil|lll/iH|i'l 


Fit:.  280.— ^  ..miu«>»i' 
all  u.  MrnncIihcU;  .i 
life  by  Dr.  Heck  of  licrliij.) 


\\  fit- 


ly derived  from  a  oomnion 
stock,  and  each  species  in 
its  ramifications  modified 
by  the  forces  and  condi- 
tions inchuhnl  unthT  the 
general  lieads  of  variation, 
heredity,  segregation,  selec- 
tion, and  the  impact  of 
environment  precisely  as 
species  in  other  groups  are 
affected.  It  is  clear  that  if 
there  is  an  origin  of  species 
through  natural  causes 
among  the  lower  animals 
and  plants,  there  is  an 
origin  of  species  among 
men.  If  homology  among 
animals  and  i)lants  is  the 
stamp  of  blood  relation- 
ship, the  same  rule  holds 
with  man  as  well.  Man  is  connected  with  tlie  lower  aninial.s 
by  the  most  perfect  of  homologies.  These  are  traceable  in 
every  bone  and  muscle,  in  every  blood   vessel  ami  glaiul.  in 

every  i)ha.<e  of  .structure, 
even  inchiding  tho.*ie  of 
the  brain  and  nervou.s 
system.  Tlir  common 
heredity  of  man  with  other 
vertebrate  animals  is  a5 
well  estal)lisln'<l  a.«<  any  fact 
in  j)hylogeny  can  l)e. 

In  working  out  the 
details  of  the  <»rigin  of 
man.  we  have  once  more 
tlie  tlire<»  '*anc«^tral  docu- 
ments "  of  biology,  conipar- 
ativ(»  anatomy,  embry<»l- 
ogy.  ami  paleontoiog^y. 
Considereti  structur- 
17     OQ,     r'    ♦  u  1  .      f  I  .w.      Jdlv,  man    forms    a    single 

Fig.  281. — Foot  skeleton  of  chiinpiiiiwH?  at  Irft,  • 

and  of  man  at  right,     (.\ftcr  Wiedor..lieim.)         gelUlS,    Iiomo,  tllC  SOlc   n»|> 

80 


454 


EVOLUTION  AND  ANIMAL  LIFE 


resentative  among  liidng  forms  of  the  Hominidse;  the  highest 
family  of  the  order  of  Primates.  To  the  species,  man,  Lin- 
naeus gave  the  scientific  name  of  Homo  sapiens,  this  being  re- 
garded by  him  as  the  primitive  species  which  has  diverged 
into  several  geographical  varieties  or  races.  Of  these,  at  least 
three  might  well  be  regarded  as  distinct  species.  The  form 
called  by  Linnaeus  Homo  sapiens  europceus  includes  not  only 
the  white  men  of  Europe,  but  allied  races  of  Africa  and  Asia, 
as  the  Moors,  the  Jews,  the  Turks,  the  Arabs,  the  Hindus 
and  the  Ainus  of  northern  Japan.     To  Homo  asiaticus  belong 


Fig.  282. — Upper  teeth  of  man  and  the  orang-utan:  At  left,  of  a  Caucasian;  in  middle, 
of  a  negro;  at  right,  of  a  grown  orang-utan.  The  condition  in  the  negro  is 
between  that  in  the  orang-utan  and  that  in  tlie  Caucasian.  (After  Wieders- 
heim.) 

the  Mongolian  races,  probably  the  Esquimaux  and  Aleuts  of 
North  America,  and  perhaps  the  American  Indians  (Homo 
americanus) ,  with  the  Malays,  the  South  Sea  Islanders,  and  the 
Australians  as  well.  Homo  afer  of  Africa  and  adjacent  islands 
comprises  the  kinky-haired  negroes  and  negritos. 

Structurally  the  members  of  the  genus  Hoino  are  closely 
allied  to  the  anthropoid  apes.  The  actual  differences  in 
anatomy  are  very  slight.  The  differences  in  degree  of  mental 
endowment  are  enormous,  but  it  can  be  shown  that  these  dis- 
tinctions are,  for  the  most  part,  of  degree  only,  associated  with 
the  greater  size  and  greater  degree  of  specialization  of  the  brain 
of  man.  Homologies  of  the  closest  sort  exist,  involving  every 
element  in  structure  as  well  as  every  function  of  the  organism 
and  every  known  mental  attribute.  The  anthropoid  or  man- 
like apes  constitute  the  family  of  Simiidae.  The  principal 
species  are  the  •following,  beginning  with  the  lowest  or  most 
monkeylike:  Hylobates,  the  gibbons,  of  several  species,  notable 


MANS   PLACi:   IX    NATL'HE 


455 


Fi«;.  2H3. —  Bnhy  nrnnR-utan. 
(Krojn  life.) 


for    their    very   loiiic    arms   and 

erect  posture;  Siamutu/a  syudur- 

ti/la,  the  sianiaii^^;  Simia  sati/rws, 

tlie     oran«i:-iitan  ;     Pan    (jorilla, 

the     jj;orilla,     soiiietinies     rallcil 

Troglodi/tcs    (/orilla    (tliou«;li    (he 

name  Trogloch/tcs  \\a.s  first  iiseil 

for    the   wren);   and    the   cliim- 

panzees,  Ayithropithcrus  iiif/rnind 

calvus.     Of   these   the  gorilla   is 

physically     the     strongest.       ll 

reaches    a    height    of    five    feet 

and   a    weiglit    of    200    pounds. 

The     chimpanzee,    smaller    and 

more     amia])le     in     dispf)sition, 

most    suggests    man    in    appear- 
ance,    although     tlie    gorilla    is 

structurally  most   like  him. 

The  Older  of  primates  lias  heen  \ariously  (•la.»<.<^ified.      It   i.s 

conveniently  divided  into  five  principal  groups:  (n)  the  lemurs 

(including   Lemuri(Ue,   Clieiromyi(he.  (laleopitlu'cida*.  and  still 

more  generalized  ex- 
tinct forms) ;  (h)  the 
I'latyrrhine  or  New- 
World  monkeys 
(Cehida*  and  Arcto- 
pithecid:e  or  Mar- 
mosets; (r)  the 
f'atarrhiiie  or  Old- 
Work  1  monkeys  and 
baboons  ((Vrropi- 
thecida-);  (</)  the 
nntliro|)oid  apes 
(Simii(hiO :  and  (r) 
Tnrin  f^IIoinini«la'). 

1.        lemurs     of 
Madagjurar   arc  the 
most     primitive. 
Like  other  primate* 
they  have  flat  n 

nnd      nn       OT'iivi?:. 


TiQ.  284. — I^rour,  furcifir. 


(.\fter  Ritjcm*  Bo».) 


456 


EVOLUTION  AND  ANIMAL  LIFE 


\ '-. 


thumb  on  each  foot.  Monkeyhke  in  their  feet  and  in  their 
general  habit,  yet  in  appearance  they  have  Uttle  to  suggest 
affinity  with  man.  In  general  make-up,  they  are  superficially 
comparable  rather  with  weasels,  squirrels,  and  bats. 

The  New- World  monkeys  differ  widely  from  the  others. 
Technically  they  are  distinguished  by  the  diverging  (platyr- 
rhine)  nostrils,  and  by  the  retention  of  the  primitively  larger 

number  of  teeth.  Many 
of  them  have  prehensile 
tails,  and  in  habit  and 
temper  all  are  very  un- 
like the  more  hardy  and 
pugnacious  monkevs  of 
the  Old  World.  Ah  the 
Old- World  monkej^s  as 
well  as  the  apes  and 
man  have  parallel  nos- 
trils, directed  downward 
(catarrhine) .  Their  tails, 
if  present,  are  not  pre- 
hensile, and  in  their 
habits  and  temper  they 
approach  progressively 
toward  man.  Catarrhine 
monkeys  are  known  to 
have  existed  in  the 
Miocene  period.  The 
anthropoid  apes  repre- 
sent a  high  degree  of 
advancement  within  the  same  group  which  finds  its  final  ex- 
treme in  the  genus  Homo. 

Considering  structural  characters  alone,  it  is  readily  con- 
ceivable that  man  should  have  had  an  anthropoid  ancestry, 
that  the  anthropoids  should  have  sprung  from  an  Old- World 
monkey  stock,  and  that  the  Old- World  monkeys  in  turn  are 
derived  from  the  lemurs.  It  is  not  supposable  that  any  living 
species  of  man  has  sprung  from  any  extant  species  of  anthropoid 
r.pe.  The  point  of  juncture  is  clearly  far  back  in  the  earlier 
Tertiary  times,  but  morphological  evidence  points  to  the  com- 
mon origin  of  primitive  man  and  the  known  anthropoids.  It  is, 
of    QQurse,  certain  that  the  intermediate  forms  when  known 


Fig.  285.— Gorilla. 


MAX'S  PLACE   IN   NATURE 


4  r^ 


will  not  be  strictly  man-apes,  nor  apo-incii,  })ut  rather  priinitivo 
creatures  unitin«i;  the  i)ossiI)iliti('s  of  hotli.  From  that  condition 
men  and  aj)es  have  since 
diverged  and  will  con- 
tinue to  diverge. 

There  is  no  doubt  of  -A 

the     truth    of     Huxley's 
statement : 


■'Thus  \vh;itever  systciii 
Oi  organs  be  studied,  the 
comparison  of  their  modi- 
fications in  the  ai>e  series 
leads  to  one  and  tlie  same 
result — that  the  strnetnral 
differences  which  sei)arate 
man  from  the  gorilla  and 
the  chimpanzee  are  not  so 
great  as  those  which  separate  the  gorilla  from  ihc  lova  i   ajn-ni.' 


In;.    USti.      i  If:i4|  of  j^Di  :iia.      ^Af'tT  iit«'iim,; 


In  fact;  as  Haeckel  has  obs'"\-<  1, 

"It  is  very  diificult  to  show  wiiy  man  shouM  not  l>e  classed  with 
the  large  apes  in  the  same  zoological  family.     Wc  al!  know  a  iimn  from 

an  ape,  liut  it  is  (|uite  an- 
other thing  to  fiiul  dilTiT- 
ences  which  are  absohile 
ami  not  of  dj'^rr''**  onlv." 


'^v^ 


iv<>^i5l 


It  nia\  Im»  l»roatlIy 
statiMJ  tliat  man  differs 
from  the  apes  in  the 
combination  of  the  ft»l- 
lowiiig  cliaracters:  (1) 
Erect  walk :  (2)  ex- 
tremities different  iatc^l 
accordingly,  the  p: 
toe  not  U'ing  op] 
able,  the  other  toes  lilih'  |»rehensile;  (3)  articulate  siHvch:  (4) 
higher  reasoning  power.  The  erect  walk  is  not  an  al>soIutc 
character.  The  higher  aju'S  walk  on  their  feet,  touching  the 
ground   at   times   with    their    knuckles.     The   taileti   nionki-ya 


i^io.  287.— Face  of  gorilla,     (.\ftcr  Brchm.) 


458 


EVOLUTION  AND  ANIJMAL  LI5^E 


volves    no 
structure. 


walk  like  a  bear^  four-footed^  and  resting  on  the  palms  of  their 
hands.  The  muscles  in  each  case  are  the  same,  although  in  man 
the  gastrocnemius  and  soleus  are  enlarged,  forming  the  calf 
of  the  leg,  while  the  expanded  gluteus  maximus  forms  the 
buttocks.  Both  buttocks  and  calf  are  scantily  developed  in 
the  apes  and  monkeys,  but  the  muscles  forming  them  are 
essentially  the  same  as  in  man. 

The  monkej^s  have  been  called  Quadrumana,  fom'-handed^ 
because  the  foot  like  the  hand  is  fitted  for  gra.sping,  and  the 

great  toe,  like  the  thumb,  is 
opposable  to  the  other  digits. 
But  as  Huxle}^  .has  clearly 
shown,  this  modification  in- 
real  change  of 
An  examination 
of  the  bones  and  muscles 
involved  at  once  shows  that 
the  hinder  limb  in  apes  and 
monkeA^s  is  truly  a  foot  and 
not  a  hand.  Part  by  part 
the  hinder  foot  of  the  mon- 
key is  homiologous  with  the 
foot  of  man,  not  with  the 
hand  (Fig.  281).  The  loss  of 
the  power  of  opposing  the 
great  toe,  on  the  part  of 
man,  is  a  result  incident  to 
the  use  of  the  hinder  limbs  for  walking  alone,  and  not  for 
grasping.  In  some  of  the  lower  races  of  man  the  great 
toe  stands  apart  from  the  others  to  a  larger  extent  than  in  the 
European  races. 

In  the  apes  there  is  a  greater  degree  of  mobility  of  the  muscles 
of  the  scalp  and  the  ear  than  in  man,  but  there  are  very  many 
cases  of  men  who  are  able  to  move  these  muscles  freely.  The 
muscles  of  the  tail  in  man  are  quite  useless,  as  are  also  those  of 
the  higher  apes,  in  which  the  coccyx  or  tail  is  scarcely  more 
developed  than  in  man. 

In  man,  the  wisdom  teeth  are  usuall}^  rudimentary,  but  in 
the  native  Australians  these  teeth  are  the  largest  of  the  series, 
as  is  also  the  case  Avith  the  apes  (Fig.  282). 

In  structure  it  is  clear  that  man  agrees  in  aU  large  matters 


Fig.  288. — A  young  gorilla  of  the  Leipsig 
Zoological  Garden.  (From  Illustrirte  Zei- 
tung,  after  a  photograph.) 


MAN'S   PLACE   IX   NATURE 


4.VJ 


with  the  anthropoid  apes,  and  tlial  lie  laiuuu    l>c  M'p:.raic<l 
an  order  from  other  primates. 

In  mental  attributes  the  differeneeh  aiu  vei y  giuia,  l»ui  li 
are  all  correlated  with  the  large  size  of  tlie  Imnu-n  brain,  and 
all  psychological  expressions  of  the  high  dcgicc  of  specii-lizalioii 
of  its  parts.  The  largest  recorded  human  ])iain,  uccoidirig  to 
Huxley,  has  a  weight  of  sixty-five  to  sixty-six  ouncj-s,  tlie 
smallest  of  about  thirty-two.  The  ])rain  of  the  Jiighoi  a|)c 
weighs  about  twenty  ounces. 

The  immense  diiTerences  betwei'u  the  iniciii^cncc  of  ajK'  and 
man  does  not  imply  any  corresi)onding  pliysical  gaj)  lietwocn 


Fig.  289. — Top  of  brain  of  a  seven-to-eiglit  months  human  em'-rv  ■•  .t  1.  fr     ■i,  ! 
year-old  female  chimpanzee  at  right,     (.\ftcr  Wi« 


f«., 


them,  or  any  corresponding  difTcTence  in  tlicir  brain.s.     Hii\ 
uses  the  illustration  of  a  watch   which  keeps  jHTfect   linie  as 
compared    with    a   watch    having   imperfect    machinery, 
difference  is  not  so  nuich  in  the  structure  of  the  watch  as  in 
the  fineness  of  the  parts  and  the  perfection  of  iheir  adju>tnp 

'Believing  as  I  do  with  C'uvier  that   the  j'  ion  of  arliru 

speech  is  the  grand  distinctive  character  of  man  nvht'ther  it  K 
lutely  peculiar  tt)  him  nr  not ).  I  find  it  very  «\'i.'<y  to  coniprehetMi  • 
some  equally  inconspicuous  .structural  difT<'rencr  may  have  Uth  tJii* 
primary  cause  of  the  inm>easnral)lc  and  practically  infmito  divt  rg-'iu-e 
of  the  Human  from  the  Simian  stirps." 


460  EVOLUTION  AND   ANIMAL  LIFE 

Huxley  further  shows  that 

"  the  brain  is  only  one  condition  out  of  many  on  which  intellectual 
manifestations  depend,  the  others  being,  chiefly,  the  organs  of  the 
senses  and  the  motor  apparatuses,  especially  those  concerned  in  pre- 
hension and  in  the  production  of  articulate  speech. '^ 

Selenka  finds  that  man  and  the  man-apes  agree  in  the  manner 
and  relation  of  the  young  in  the  mother-body  to  that  body  in 
that  both  man  and  man-apes  have  but  a  single  disclike  placenta, 
while  the  other  apes  have  two  opposed  disc  placentas.  And 
Friedenthal  finds  that  while  the  blood  serum  of  man  is  poisonous 

to,  and  destroys  the  red 
blood  corpuscles  of  all 
other  animals  experi- 
mented on,  these  animals, 
including  fishes,  amphib- 
ians, .reptiles,  birds,  and 
mammals,  among  which 
T?     onn    T>-  u+  V,     1   ^  1  f*      J   •  1,+  f    +  +     latter    were    lemurs    and 

Fig.  290. — Right  hand  at  left,  and  nght  foot  at 

right,   of   a    two-months-old    human   embryo,  NeW-World       {AtelcS      and 

showing    similar    position    of    the    first    digit  PithecOSClUrUs)     and     Old- 

(thumb,  great  toe)  in  each.     (After  Wieders-  ixr        i   i     //^  77 

i^gi^^)  World  {Cynocephalus, 

Macacus  and  Rhesus) 
monkeys,  it  does  not  injure  the  corpuscles  of  the  man-apes 
(orang,  gibbon,  and  chimpanzee).  This  immunity  exists  only 
among  closely  related  animals  as  the  horse  and  donkey,  dog 
and  wolf,  and  hare  and  rabbit.  From  which  it  is  evident  that 
man  and  the  man-apes  have  nearly  identical  blood. 

The  second  "ancestral  document,^'  embryology,  emphasizes 
the  common  origin  of  man  with  that  of  the  higher  vertebrates 
and  notably  with  that  of  the  anthropoids.  The  embryos  of 
man  and  apes  develop  in  a  fashion  precisely  parallel.  In  both, 
as  in  all  other  mammals,  the  early  presence  of  gill  slits  furnishes 
evidence  of  a  descent  from  a  fishlike  ancestry.  The  same 
evidence  is  given  in  the  embryonic  growth  of  reptiles  and  birds. 
In  the  development  of  the  human  child  some  simian  traits 
appear,  these  being  wholly  or  partly  lost  in  the  more  advanced 
stages.  Among  these  is  the  lanugo  or  general  covering  of  long 
hairs,  more  or  less  developed  in  certain  stages  of  fcetal  growth, 
but  lost  entirely  before  birth.     The  curving  upward  of  the  feet, 


MAN'S   PLACE   IN   NATIIJE 


401 


characteristic  of  early  cliiklliood,  is  a  simian  trait.  According 
to  Jeffreys  Wyman,  when  the  foetus  is  about  an  inch  in  Icnptli, 
"the  great  toe  is  shorter  than  the  otliers,  and  instead  of  Ix-in^ 
parallel  to  them,  is  projected  at  an  an^lc  from  the  side  of  tlic 
foot,  thus  corresponding  with  the  j)erman('nt  condition  rjf  thi^ 
part  in  the  Quadruniana/' 

The  great  grasping  jjowcr  of  young  l)ahios  is  well  known, 
and  this  is  hkewise  a  simian  trait. 
Dr.  Louis  Robinson  has  shown  that 
very  young  babies  will  su})port  tlieii- 
own  weiglit,  by  holding  to  a  hori- 
zontal bar  for  a  j^eriod  of  half  a 
minute  to  two  minutes.  In  all  cases 
"the  thighs  are  bent  nearly  at  riglit 
angles  to  the  body  and  in  no  cas(^ 
did  the  lower  limbs  hang  down  and 
take  the  attitude  of  the  erect  j^osi- 
tion''  (Fig.  291). 

The  study  of  embryonic  develoj)- 
ment  shows  also  that  the  tail  in 
man  and  ape  alike  is  at  a  certain 
stage  of  development  longer  than  the 
legs,  as  in  the  monkeys  and  otlier 
lower  mammals.  In  this  stage,  ac- 
cording to  Romanes,  "the  tail  ad- 
mits of  being  moved  by  nuiscles 
which  later  on  dwincUe  away." 
Sometimes,  however,  these  muscles 
persist  througli  life. 

The  vermiform  appendix  is  like- 
wise more  developed   in   tlie   human 

embryo  than  in  the  adult,  a  fact  wliicli  holds  in  regard  to 
vestigial  structures  generally.  As  already  statcMl  in  Chapter 
XX  (discussion  of  vestigial  structures),  Wiedersheini  hiis  re- 
corded in  man  ISO  structural  remini.scences  of  l»is  di»:»rent  fnuii 
the  lower  animals.  All  the  facts  of  tliis  chiss  i><)int  to  a  coinnum 
origin  of  man  and  apes,  and  an  earlier  community  of  origin 
with  other  mammals  and  with  other  vertebrates,  the  most 
primitive  traits  allving  all  of  them  witli  the  fi.shes. 

Paleontolou^v  has  comparatively  little  to  «>frer.  but  that  httic 
is  decisive.     Tlie  life  habits  of  men  and  rnonkev^  nm  sin-tdnrlv 


ii(j.    -'Ul.  — An 
iniititlis     ol«i     ~ 
weinht  for  t»Vfi 
the    attiludr    of     the 
linibii     in     utrnriRrly 
(From  )'. •         ■''■ 


iiiiant     tlirra 


luwrr 


462 


EVOLUTION  AND  ANBIAL  LIFE 


unfavorable  to  the  preservation  of  their  remains  as  fossils  in 
rocks.  Of  the  hundreds  of  species  and  millions  of  individuals 
of  the  monkey  tribes,  very  few  of  their  remains  are  known 
anywhere.  Living  in  thickets  and  underbrush  there  is  little 
opportunity  for  them  to  be  preserved  as  fossils.     With  man, 


Fig.  292. — End  of  the  humerus  of  various  animals  including  man,  showing  position  of 
the  humerus  canals.   yl,Hatteria;  i?,  Lacerta;  C,  cat;  Z),  man.    (After  Wiedersheim.) 

the  condition  is  not  very  different.  Implements  of  stone,  bone, 
bronze,  and  iron  mark  stages  in  the  development  of  primitive 
tribes.  Fossil  remains  are  confined  almost  wholly  to  bones 
buried  in  quicksand  or  in  the  drippings  of  caves.  Of  fossil 
monkeys,  several  genera  have  been  described.  Pan  sivalensis 
is  a  species  of  extinct  gorilla  from  the  Pliocene  of  the  Punjaub. 

Of  all  the  fossil  primates 
the  one  of  the  greatest 
interest  is  Pithecanthropus 
erectics,  from  the  upper 
Pliocene  of  Java,  lately 
described  by  Dr.  Eugene 
Du  Bois.  This  species 
has  been  designated  by 
Haeckel  as  "  the  last  link  " 
in  human  genealogy.  Its 
characters  have  been  held 
to  correspond  with  those 
of  the  hypothetical  ape- 
man  imagined  by  Haeckel  and  named  Pithecanthropus  alaulus, 
before  these  remains  were  found.  The  generic  name  of  the 
imaginary  ape-man  has  been  transferred  to  the  actual  fossil. 
The  discovered  relics  of  this  species  are  scanty  enough,  consist- 
ing of  the  skullcap,  a  femiu-,  and  two  teeth  (Figs.  294  and  295). 


a.  Ps. 


Fig.  293. — The  human  eye  showing,  Ps,  arrange- 
ment of  the  third  eyelid,  Blica  semilunaris. 


MAN'S  f^LACE  IX  NATTT^K 


4C3 


In  Haeckers  Cambridge  lectuiv,  ''T\w  L:ut  Link,"  the  facts 
concerning  this  fossil  are  thus  sniinned  up: 

"The  remains  in  question  rested  uimii  a  eonRlomorato  which  lies 
upon  a  bed  of  marine  marl  and  sand  of  IMioceiie  A^e.     Together  with 
the  bones  of  Pithecanthropus  were  found  those  of  Stegoilou,  Ix>ptolxw, 
Rhinoceros,  Sus,  Felis,  Hyajna,  lIij)iioi.ni;nnus,  Tapir,  KIcpha-s,  and  a 
gigantic  Pangohn.     It  is  re- 
markable that  the  first  two 
of  these  genera  are  now  ex- 
tinct, and  that  neitlier  hip- 
popotamus nor  liya}na  exists 
any   longer    in   the   oriental 
region.      If    we    may    judge 
from    these    fossil    remains, 
the  bones  of  Pithecanthropus 
are   not    younger   than    the 
oldest  Pleistocene  and  prol)- 
ably  belong   to    the    Upper 
PHocene.    The  teeth  are  very 
like  those  of  man.     The  fe- 
mur also  is  very  human,  but 
shows  some   resemblance  to 
that  of  the  gibbons.     Its  size, 
how^ever,  indicates  an  animal 
which  stood  when  erect  not 
less  than  five  feet  six  inches 
high.     The  skullcap  is  very 
human,  but  wuth  very  promi- 
nent   eyebrow     ridges,    like 
those  of  the  famous  Neander- 
thal cranium.    It  is  certainly  not  that  of  an  idi«)i.    h  iiad  an  t-sumaUHi 
cranial  capacity  of  about  1,(K)0  c.c.,  tliat  is  to  siiy,  much  larpi^r  than 
that  of  the  largest  ape,  which  posscsst^s  not  more  than  fi()0  c.c.     The 
crania  of  female  Australians  and  V(>ddahs  measure  not  more  than  1,100 
c.c,  some  even  less  than  1,()(K)  c.c;  but  as  these  Veddah  woiiu'ii  staiu! 
only  about  four  feet  nine  inches  higli,  the   eoinputeii  cranial  •  ty 

of  the  much  taller  Pithecanthropus  is  comparatively  low  indeeti. 


Fin.  291.  -  Ufinniiis  of  /" 

tlic  »iiiiKlc  femur  ithowii  in  difllerTnt  «a|wcts 
(I  roin  'The  Open  Court.") 


The  impressions  left  by  the  cerebral  coiivolution.s  an*  ab*<J 
very  human^  more  highly  develope*!  tiuiu  in  tlie  reoi*nt  a\w^. 


464 


EVOLUTION  AND  ANIMAL  LIFE 


It  is  stated  that  in  the  discussion  at  Leyden,  where  D]-. 
Du  Bois's  specimens  were  first  exhibited,  "three  of  the  twelve 
experts  present  held  that  the  fossil  remains  belonged  to  a  low 
race  of  man;  three  declared  them  to  be  those  of  a  m^anlike  ape 
of  great  size,  the  rest  maintained  that  they  belonged  to  an 


Fig.  295. — Cranium  of  Pithecanthropus  erectus.      (From  WeHall  u.  Menschheit.) 


intermediate  form,  which  directly  connected  primitive  man 
with  the  anthropoid  apes.'^     (Haeckel.) 

Of  the  several  early  relics  which  are  distinctly  human,  the 
Neanderthal  skull,  found  by  Professor  Schaffhausen  in  a  lime- 
stone cave  in  the  Neanderthal,  near  Diisseldorf,  is  the  most 
notable.  This  skull  represents  the  most  primitive  and  least 
specialized  of  any  skull  type  known  to  be  distinctty  human. 
It  has  therefore  been  recently  named  as  a  distinct  species  of 
man,  Homo  neanderthalensis. 

According  to  Huxley,  this  type  of  man,  while  certainly 
simple,  primitive,  and  doubtless  extremely  barbarous  is,  never- 
theless, wholly  human.  It  shows  no  distinctly  pithecoid  char- 
acters, and  it  belongs  clearly  to  the  genus  Homo. 

Another  skull  of  great  antiquity  comes  from  a  cave  at 
Engis  in  the  valley  of  the  Meuse,  and  is  know^n  as  the  Engis 
skull.  This  was  found  associated  with  bones  of  the  mammoth 
and  of  the  woolly  rhinoceros.    This  also  is  extremely  primitive. 


MAN'S  PLACE  IN    NATIRF. 


40 


K> 


suggesting  the  skull  of  an  EthioiMan.     It  is,  liowovor,  more 
like  that  of  recent  man  than  is  the  Neanderthal  skull. 

The  comparison  of  the  different  races  of  men  through  the 
methods  of  the  science  of  ethnology  throws  much  light  on  the 
relations  of  the  races  to  one  another,  hut  casts  little  light  on 
.;:he  origin  of  the  genus  Homo.  This  study  considerahly  in- 
creases the  number  of  primitive  races  beyond  tl»e  three  stenw 
usually  recognized  or  the  four  named  by  Linnu'us.  The  form 
of  the  skull,  the  color  of  the  skin,  the  character  of  the  hair,  j-.nd 
the  traits  of  language  have  given  rise  to  the  technical  nomen- 
clature of  numerous  more  or  less  well-delined  groups.     These 


'^\t'  B^"' 


\G.  296. — Remains  of  the  Nenn<lerfhnl  man  in  the  Provincial  Mu-. 


H-.Mn. 


races  of  men  limited  by  geographical  segregation  run  more  or 
less  distinctly  parallel  to  the  races  or  geographical  sul^siHu-it^ 
\vithin  widelv  distributed  sjHH'ies  of  animals.  Our  knowleiipo 
of  the  origin  of  man  as  derived  from  ethnology  is  thiw  summe«l 
vp  by  Huxley:  "iSo  far  a.^  the  lig^^  '-•  hri-hr  it  show?  him  sub- 


466 


EVOLUTION   AND  ANIMAL  LIFE 


Fig.  297. — Skull  of  ancient  man  from  Spy 
in  Belgium.  (From  Weltall  m.  Menschheit; 
after  Professor  Fraipont's  photograph  of 
the  original  in  the  musem  at  Liege.) 


stantially  as  he  is  now,  and  when  it  grows  dim  it  permits  us  to 
see  no  sign  that  he  was  other  than  he  is  now.'' 

The    gradual    development    of    man    from    nomadic    apes; 
the  gradual  effect  of  the  prolonged  infancy  of  his  young  in  the 

holding  of  the  family  to- 
gether; the  altruistic  trans- 
formation of  the  family  into 
the  patriarchal  and  tribrJ 
systems;  the  gradual  in- 
crease of  the  power  of  choice 
among  instincts,  a  develop- 
ment which  at  last  places 
intellect  above  instinct,  the 
use  of  fire  and  the  use  of 
tools,  the  growth  of  speech 
and  its  reaction  upon  intel- 
ligence, the  invention  of 
writing,  effects  of  the  su- 
premacy of  the  strong — all 
these  matters  afford  large 
range  for  speculation  and  some  opportunity  for  direct  investi- 
gation. But  the  essential  fact,  the  kinship  of  man  with  the 
lower  forms,  and  his  divergence  from  them  through  the  opera- 
tion of  natural  laws,  forces  and  conditions  more  or  less  per- 
fectly understood,  all  this  must  now  be  taken  as  settled  by  the 
investigations  and  dis- 
coveries of  Darwin  and  his 
coworkers  and  successors. 

Assuming  that  the  gene- 
alogy of  man  can  be  traced 
through  the  anthropoids 
and  the  Old- World  mon- 
keys to  the  lemurs,  how 
much  further  can  we  go? 
Apparently  the  lemurs  rep- 
resent an  early  offshoot 
from  the  mammalian  stock, 

the  nearest  point  of  juncture  being  the  order  of  marsupials,  now 
so  largely  represented  in  Australia.  Certain  extinct  lemurian 
genera  are  more  distinctly  primitive  than  any  of  the  living 
forms,    The  marsupials  are  connected  with  the  primitive  group 


Fig.  298. — Diagrammatic  representation  of 
profiles  of  crania  of  primitive  types  of  man. 
(After  Leiaormant.) 


MAN'S  PLACE  IX  NATURE  4«7 

of  reptile-mammals,  the  ]\lonotr(Mnes  (Ornithorhyuchus,  Tachy- 
glossus),  now  also  represented,  although  scantily,  in  Australia. 
The  Monotremes  may  be  assumed  to  be  derived  from  reptilian 
stock,  perhaps  from  ancestors  of  the  three-eyed  lizards  of  New 
Zealand,  known  as  Sphenodon  or  llatteria.  Behind  these 
lizards  we  certainly  find  the  jjrimitive  aniphil)ian.s  or  nmilcd 
frogs  and  behind  these  the  group  of  lung-bearing  fi.slies,  known 
as  fringefins  or  crossopter3'gians.  These  fishes  were  originally 
derived,  no  doubt,  from  sharks,  and  the  sharks  may  have 
come  from  wormlike  forms  through  intermediate  groups  wlii<-h 
find  their  nearest  modern  homologues  in  the  lamprey  and 
lancelet,  and  possibly  in  the  wormhke  acorn-tongue  or  balano- 
glossus,  a  creature  which  to  a  soft  wormlike  body  adds  the  gill 
slits  of  a  vertebrate  and  a  trace  of  a  primitive  backUjue  or 
notochord.  Haeckel  goes  on  with  confideuen  to  show  the 
derivation  of  one  type  of  worm  from  another,  of  all  from  allies 
of  the  hydra  and  volvox,  then  from  tlie  one-celled  amcrlui, 
and  at  last  from  the  still  more  jirimitive  monera,  a  micro- 
scopic bit  of  protoplasm.  ]^ut  witii  every  step  I  jack  ward  the 
genealogy  grows  more  and  more  hy})othetical.  All  sorts  of 
possibilities  open  at  every  turn  and  j^ositive  proof  is  nece.ss:irily 
lacking.  The  gill  slits  and  the  primitive  notochord  of  the  human 
embr3"0  leave  little  doubt  that  man  in  conunon  with  all  other 
vertebrates  had  a  fishlike  ancestry.  In  the  line  of  this  ancestry 
must  have  lain  the  extinct  crossopterygian  fishes,  but  U'hind 
this  there  is  room  all  the  way  for  serious  doubt  and  (piestioninR. 

This  much  is  certain,  man's  place  is  in  nature.  Ho  is  part 
and  parcel  of  nature,  and  the  forces  that  still  act  on  flower  and 
bird  and  beast  are  the  forces  by  which  the  central  <'nergy  of 
the  universe,  whatever  its  name  or  dt^finition,  each  day  "ifi- 
stantly  and  constantly  renews  tlie  work  of  creation." 

Objections  have  been  raised  to  the  theory  of  the  descent  of 
man  from  the  lower  primat(»s  on  grountls  sup|K)se*l  to  find  tiieir 
sanction  in  theology.  Such  objections  have  no  standing  in 
science.  In  Darwin's  words:  "Theology  and  science  must  «'m'». 
run  its  own  course  and  I  am  not  res|>onsible  if  their  nunn...^ 
point  be  still  afar  ofT."  In  the  long  run.  thwlogy.  with  other 
forms  of  philosojihy.  nnist  adjust  itself  to  harmonize  with 
ascertained  trutli.  Tli(>  origin  of  in.an  is  m)t  a  (juestion  "<"  '-  ''- 
sonal  preference  nor  one  lo  be  decided  by  a  majority  vot«-. 
only  question  is  as  to   what   is  true.     "  K.xtinguishiM  •»->u1q- 


468  EVOLUTION  AND  ANIMAL  LIFE 

gians,"  Huxley  tells  us,  "lie  about  the  cradle  of  every  science 
as  the  strangled  snakes  beside  that  of  the  infant  Hercules.'' 
Looking  along  the  history  of  human  thought,  we  see  the  attempt 
to  fasten  to  Christianity  each  decaying  belief  in  science.  Every 
failing  scientific  notion  has  claimed  orthodoxy  for  itself.  That 
the  earth  is  round,  that  it  moves  about  the  sun,  that  it  is  old, 
that  granite  ever  was  melted — all  these  beliefs,  now  part  of  our 
common  knowledge,  have  been  declared  contrary  to  religion, 
and  Christian  men  who  knew  these  things  to  be  true  have  suf- 
fered all  manner  of  evil  for  their  sake.  We  see  the  hand  of  the 
Almighty  in  nature  everywhere ;  but  everywhere  he  works  with 
law  and  order.  We  have  found  that  even  comets  have  orbits; 
that  valleys  were  dug  out  by  water,  and  hills  worn  down  by 
ice;  and  all  that  we  have  ever  known  to  be  done  on  earth  has 
been  done  in  accordance*  with  law. 

Darwin  says:  "To  my  mind  it  accords  better  with  what  we 
know  of  the  laws  impressed  on  matter  by  the  Creator,  that  the 
production  and  extinction  of  the  past  and  present  inhabitants 
of  the  world  should  have  been  due  to  secondary  causes,  like 
those  determining  the  birth  and  death  of  an  individual.  When 
I  view  all  beings,  not  as  special  creations,  but  as  lineal  descend- 
ants of  some  few  beings  who  lived  before  the  first  bed  of  Silurian 
was  deposited,  they  seem  to  me  to  become  ennobled.  There 
is  grandeur  in  this  view  of  life,  with  its  several  powers  having 
been  originally  breathed  by  the  Creator  into  a  few  forms  or 
into  one,  and  that  while  this  planet  has  gone  cycling  on  accord- 
ing to  the  fixed  law  of  gravity,  from  so  simple  a  beginning, 
endless  forms  most  beautiful  and  most  wonderful  have  been 
and  are  being  evolved." 

With  the  growth  of  the  race  has  steadily  grown  a  concep- 
tion of  the  omnipotence  of  God.  Our  ancestors  felt,  as  many 
races  of  men  still  feel,  that  each  household  must  have  a  god  of 
its  own,  for,  numerous  as  the  greater  gods  were,  they  were 
busy  with  priests  and  kings.  Men  could  hardly  believe  that  the 
God  of  their  tribe  could  be  the  God  of  the  Gentiles  also.  That 
He  could  dwell  in  the  temples  not  made  with  hands  removed 
Him  from  human  sight.  That  there  could  be  two  continents 
was  deemed  impossible,  for  one  God  could  not  watch  them  both. 
That  the  earth  was  the  central  and  sole  inhabited  planet  rested 
on  the  same  Hmited  conception  of  God.  That  the  beginning 
of  all  things  was  a  few  thousand  years  ago  is  another  phase  of 


MAN'S  PLACE   L\   NATURE  409 

the  same  limitation  of  view,  as  is  the  idea  of  tlie  sjxjcial  inechan- 
ical  creation  for  every  form  of  animal  and  plant. 

A  Chinese  sage,  wliose  words  remain  thougli  his  name  Ix; 
lost  in  mists  of  the  ages,  has  said:  "  lii;  cannot  be  concfiilcil : 
He  will  appear  witliout  showing  Himself,  cfTect  renovation  with- 
out moving,  and  create  perfection  williout  acting.*  It  i.s  tlie 
law  of  lieaven  and  earth,  whose  way  is  solid,  sub.stantial,  va,st, 
and  unchanging/' 


81 


APPENDIX 


References  .to  general  and  sijocial  treatFiu-nts  of  tlio  s\il)j<Tt«  in- 
cluded ill  this  book,  aiTanji;ed  accordinjr  to  ehaj)ter8.  Tljos<'  rffrn-mi'M 
are  confined  to  books  and  papers  pul)Iishe(l  in  Knglisli  (inciiuliiiK  traitM- 
lations  of  foreign  works)  and  are  intended  for  the  assistance  of  p'ru-ral 
readers  and  elementary  students  wishing  to  follow  up,  in  more  dotnil 
than  is  offered  in  this  book,  the  study  of  any  particular  phas<^  of  the 
general  subject  of  Evolution.  These  references  are  therefore  mostly 
not  to  original  papers,  but  to  manuals,  sun»mari<'S,  and  digests  of 
evolution  subjects.  The  list  makes  no  attempt,  of  course,  to  include 
all  of  even  the  most  general  works  of  reference. 

ChAI'TEK     I.      KVOH  TION     J)KFINEn. 

Spencer:  Principles  of  Biology,  vol.  I,  ])art  iii,  IS?').  (Virm:  Kvfihition 
of  To-day,  pp.  1-21,  ISSO.  Le  ('onto:  l:]volution,  Its  Xatun*,  lu* 
Evidences,  and  Its  Relation  to  K<'ligious  Thought,  pp.  li-'M.  1^S.S. 
Haeckel:  History  of  Creation,  vol.  I,  eh.  i.  1^(L'.  Miirshail:  Dar- 
winian Theory,  pp.  1-24,  1894.  Williams:  (Icologii-al  Hiolog^*, 
pp.  371-3S4,   1S95.     Romanes:  Darwin  and  .\ft(T  Danvin,  v<»l. 

I,  pp.  12-22,  1896.  Marshall:  Biological  Ix^ctunvs,  pp.  l-2f>, 
1897.  Howison:  Limits  of  Evolution,  pp.  12-1^,  19()1.  Huxley: 
Darwiniana,  1894. 

Chapter   II.     Variety  and  Unity  ok  Life. 
Jordan:  Footnotes  to  Evolution,  ch.  i  and  ii,  l'.K)2. 

Chapter  III.     Life,  Its  Physical  Basis  and  Simplest  Expression*. 

Verworn:  General  Physiology,  1899.  Wilson:  Chaptt-rs  on  Evolution, 
pp.  61-79,  1883.     Haeckel :  History  of  Creation,  vol.  I,  ch.  xv ;  vt.l. 

II,  ch.  xvii  and  xviii,  1892.  Huxley:  On  the  Physical  B:u<is  of 
Life  (ch.  iii,  in  Essays  on  Method  and  Results).  Marshall:  Bio- 
logical Lectures,  pp.  114-191,  1S97.  Conn:  The  MciIkkI  of  Evo- 
lution, ch.  ix,  1900.  Jordan  and  Kellogg:  Animal  Life.  ch.  i,  ii,  an«i 
iv,  1900.  McFarland:  The  Physical  Basis  of  Hcrdity.  ch.  vi  in 
Jordan's  Footnotes  to  Evolution,  1902.  Wilson:  The  Cell  in 
Development  and  Inheritance,  2d  ed.,  190-1.  Wci<;mann:  The 
Evolution  Theory,  vol.  II,  Lect.  36,  1904. 

471 


472  APPENDIX 

Chapter  IV.    The  Factors  and  Mechanism  of  Evolution. 

Darwin:  Origin  of  Species,  ch.  xv,  1859.  Spencer:  The  Factors  of 
Organic  Evolution,  pp.  1-37,  1889.  Gray:  Darwiniana,  pp.  9-61, 
1889.  Conn:  The  Method  of  Evolution,  1900.  Cope:  Primary 
Factors  of  Organic  Evolution,  1896.  Jordan:  Footnotes  to 
Evolution,  ch.  iii  and  iv,  1902.  Weismann:  The  Evolution 
Theory,  vol.  I,  Lect.  1,  1904. 

Chapter   V.     Natural   Selection   and   the   Struggle   for 

Existence. 

Malthus :  Principles  of  Population.  Darwin :  Origin  of  Species,  ch. 
iii  and  iv,  1859.  Wallace:  Darwinism,  pp.  14-125,  1891.  Mar- 
shall: Lectures  on  the  Darwinian  Theories,  pp.  27-52,  1894.  Ro- 
manes: Darwin  and  After  Darwin,  vol.  I,  pp.  125-294,  1895. 
Wallace:  Natural  Selection  and  Tropical  Nature,  1895.  Bailey: 
Survival  of  the  Unlike,  pp.  13-54, 1897.  Osborn :  From  the  Greeks 
to  Darwin,  ch.  vi,  1899.  Headley:  Problems  of  Evolution,  pp. 
68-155,  1901.  Conn:  Method  of  Evolution,  ch.  ii  and  iii,  1901. 
Morgan:  Evolution  and  Adaptation,  ch.  iv  and  v,  1903.  Weis- 
mann: The  Evolution  Theory,  vol.  I,  Lects.  2  and  3,  1904.  De 
Vries:  Species  and  Varieties,  Their  Origin  by  Mutation,  ch.  xxviii, 
1905.  Metcalf:  Organic  Evolution,  1905.  Kellogg:  Darwinism 
To-day,  1907. 

Chapter  VI.    Artificial  Selection. 

Darwin:  Origin  of  Species,  ch.  i,  1859.  Darwin:  Animals  and  Plants 
under  Domestication,  vols.  I  and  II,  1868.  Wallace :  Darwinism, 
ch.  iv  and  vii,  1891.  Burbank:  New  Creations  in  Fruits  and 
Flowers  (catalogues  of  plant  novelties),  1893  and  succeeding 
years.  Marshall:  Lectures  on  the  Darwinian  Theories,  pp. 
27-36, 1894.  Romanes :  Darwin  and  After  Darwin,  vol.  I,  pp.  294- 
314,1896.  Bailey:  Survival  of  the  Unlike,  1897.  De  Vries:  Spe- 
cies and  Varieties,  Their  Origin  by  Mutation,  1905.  Bailey :  Plant 
Breeding,  4th  ed.,  1906.  Harwood :  New  Creations  in  Plant  Life, 
1906. 

Chapter  VII.    Theories  of  Species-forming  and  Descent 

Control. 

Eimer:  Organic  Evolution,  1890.  Romanes:  Darwin  and  After  Dar- 
^\^n,  III,  1897.  Conn :  Method  of  Evolution,  ch.  vii  and  viii,  1900. 
Packard:  Lamarck,  His  Life  and  Work,  1901.  Morgan:  Evolu- 
tion and  Adaptation,  1903,    Weismann;  The  Evolutionary  Thf^r 


APPENDIX  473 

ory,  vol.  II,  Lefts.  32  to  3"),  KMM.  I\.  Vrics:  S|m  . ;.  ^  •ui  Vani- 
ties, Their  Origin  by  Mutation,  IIKJ.').  Kello^i;:  i»vv'  - 
To-day,  11)07. 

Chapter  VIII.     CiEOfJH.^i-nir  Isolation-  .\.\d  ^J•KrI^•.^-^•r)RM^^•o. 

Wallace:  Darwinism,  pp.  33.S-374,  ISDl.  Honian.s:  Darwin  an.l 
After  Darwin,  I,  j)p.  204-24S,  IS!).",.  W.-Jsniann:  'IIm-  livduti-.-, 
Theory,  vol.  II,  I^ct.  32,  VM)\.  .Jordan:  The  Ori^rin  of  SjM-n.s 
through  Isolation,  Science,  N.  S.,  vol.  xxii,  pp.  54r>-.'ir.2,  VMl't. 
Gulick:  Evolution,  ILieial  and  Hahitudinal,  ItK)').  Montgonjery: 
Analysis  of  llacial  Descent  in  Animals,  WHn). 

Chapter   IX.     Variation-   and   Mitation'. 

Darwin:  Origin  of  Species,  ch.  i,  ii,  and  v,  is;,!).  Darwin:  Animals 
and  Plants  Under  Domestication,  vols.  I  and  II,  1S(>S.  WiUin: 
Chapters  on  Evolution,  i)p.  121-112,  1.SS3.  Wallace:  Darwinism, 
ch.  iii  and  iv,  1891.  Bateson:  Materials  for  the  Study  of  N'aria- 
tion,  1894.  Romanes:  Darwin  and  Aft<T  Darwin,  vol.  I,  pp. 
50-65,  pp.  120-135,  189r).  Rumpus:  Variation.s  and  .Mutations 
of  the  Introduced  Sparrow,  in  Hiological  IxM-turi'S,  Wo<hI'.s  H.hII, 
pp.  1-15,  1896-97.  liiometrika:  A  Journal  of  Variation,  19()l — 
to  date.  Vernon:  Variation  in  Plants  and  -Animals,  PKi3.  Mor- 
gan: Evolution  and  Adaptation,  P.K)3.  Kellogg  and  Ii<'ll:  Studies 
of  Variation  in  Insects,  1904.  Davenport:  Statistical  Meth<MLs, 
2d  ed.,  1904.  De  Vries:  Speeies  and  Varieties  and  Their  Ongin 
by  Mutation,  1905. 

Chapter   X.     Heredity'. 

Brooks:  Heredity,  1883.  Weismaiui:  Essiws  upon  Heredity,  vol.  I, 
Lects.  4  and  6,  1891;  Essays  upon  Heredity,  vol.  II,  ch.  xii,  1S92. 
Marshall:  Biological  Lectures,  pp.  151>-191,  1^97.  (i.ilton: 
Natural  Inheritance,  1S99.  Coini:  Method  of  Evolution,  pp. 
101-156,  1901.  Bateson:  Mendel's  Principles  of  HenMJity,  VXY2. 
Redfield:  Control  of  Heredity.  P.)02.  Wilson:  llie  (Vll  in  Dp- 
velopment  and  Inheritance,  2d  ed.,  \\HV\.  Montgt)nu'ry :  .Xnalysis 
of  Racial  Descent  in  Animals,  19(X>.  \\  (hkIs:  Heredity  in  Royally, 
1906. 

Chapter  XI.    The  Inhehitance  of  Acquired  Characters. 

Weismann:  Essays  on  Heredity,  vol.  I,  1000.  Spenccr-Weisniann ; 
Contemporary  Re\'iew,   May-DecemU-r,   1S93;  Septoniber-Orto- 


474  APPENDIX 

ber,  1895.  Cope:  Pnmary  Factors  in  Organic  Evolution, pp.  397- 
473,  1896.  Marshall:  Biological  Lectures  and  Addresses,  pp. 
91-115, 1897.  Hutton:  Darwinism  and  Lamarckism,  1899.  Weis- 
mann :  The  Evolution  Theory,  vol.  II,  Lects.  23  and  31, 1904.  Met- 
calf:  Organic  Evolution,  pp.  67-82,  1904.  Kellogg:  Darwinism 
To-day,  ch.  x. 

Chapter   XII.     Generation,  Sex,  and  Ontogeny. 

Marshall:  Lectures  on  the  Darwinian  Theories,  pp.  78-115,  1894. 
Geddes  and  Thomson:  The  Evolution  of  Sex,  1889.  Romanes: 
Darwin  and  After  Darwin,  vol.  I,  ch.  iv,  1896.  Marshall:  Bio- 
logical Lectures  and  Addresses,  jDp.  289-363,  1897.  Jordan  and 
Kellogg :  Animal  Life,  ch.  v,  1900.  Morgan:  Regeneration, 
.1901.  Weismann:  The  Evolution  Theory,  vol.  I,  Lects.  13  to 
16;  vol.  II,  Lects.  27  to  30,  1904.  Wilson:  The  Cell  in  Develop- 
ment and  Inheritance,  2d  ed.,  1904.  Montgomery:  Analysis  of 
Racial  Descent  in  Animals,  1906.  Morgan :  Experimental  Zoology, 
1907. 

Chapter   XIII.     Paleontology. 

Wilson:  Chapters  in  Evolution,  ch.  xvi,  1883.  Wallace:  Darwinism, 
ch.  xiii,  1891.  Marshall:  Lectures  on  the  Darwinian  Theories, 
pp.  53-77,  1894.     Williams:   Geological  Biology,  pp.  1-9,  78-110, 

1895.  Romanes:   Dar\vin  and  After  Darwin,  vol.  I,  pp.  156-203, 

1896.  Le  Conte:  Elements  of  Geology,  part  III,  1891.  Smith: 
Evolution  of  Fossil  Cephalopoda,  ch.  ix,  in  Jordan's  Footnotes  to 
Evolution,  1902.     Metcalf :  Organic  Evolution,  pp.  103-111,  1905. 

Chapter  XIV.     Geographical  Distribution. 

Wallace:  The  Geographical  Distribution  of  Animals,  1876.  Wallace: 
Island  Life,  1880.  Heilprin:  Geographical  Distribution  of  Ani- 
mals, 1887.  Wallace:  Dar^^dnism,  pp.  338-374,  1891.  Beddard, 
Zoogeography,  1895.  Romanes:  Darwin  and  After  Darwin,  vol. 
I,  pp.  204-248,  1895.  Jordan:  Science  Sketches,  pp.  83-132. 
Wallace:   The  Malay  Archipelago,  2d  ed.,  1869. 

Chapter  XV.     Adaptations. 

Semper:   Animal   Life,    1881.     Morgan:   Evolution   and   Adaptation, 

1903.  Weismann :  The  Evolution  Theory,  vol.  I,  Lects.  5  and  7, 

1904.  Jordan :   Guide  to  the  Study  of  Fishes,  vol.  I,  ch.  xi  and  xii, 

1905.  Folsom:  Entomology,  with  Reference  to  Its  Biological 
and  Economic  Aspects,  1906. 


APrK.NDix  475 

Chapter  X\\.     Parasitism   and   I)K<iKNKRATi<iN. 

"^"^^llsoii:  Chapters  on  Evolution,  jij..  .'M'J-.'Ul'),  \SKi.  Viui  iVnHrn: 
Animal  I'arasitcs  and  Messmates,  ISV.I.  l>ciinK>r,  M;u^trt  aiul 
Vandervelde:    Involution  by  Atropliv,  1S?H». 

\^HAPTER  XVII.       MlTl  AI,  Am  AND  CoMMrNAI,  I. IKK  AMr»\r,  AmMMJ*. 

Wilson:  Chapters  on  Involution,  «h.  xiii,  lS.s;i.  Van  li<ne<len:  Ani- 
mal Parasites  and  Messmates,  ISS'.J.  Kropotkin:  Mutual  Aid, 
11)02.  Weismann:  The  Evolution  Theory,  vol.  I,  Ix- •  "  "MVl. 
Kellogg:    American   Inserts,  j)p.    1'XV  "idl,    11H).'». 

Chapter   X\111.     Color   a.nd   Pattkr.n    in    Animaij*. 

Poulton:  The  Colors  of  Animals,  ISOO.  P.c<ldard:  Annual  Coloration, 
1895.     Wallace:    Natural   Selection   and   Tropical   Nature,  ch.  v, 

1895.  Newbigin:  Colors  in  Nature,  1S<>S.  \\'ti>-mann :  'Hio 
Evofutionary  Theory,  vol.  1.  Pects.  4  and  5,  P.H>1.  Keljo^: 
American  Insects,  cli.  xvii,  P.  10."), 

Chapter   XIX.     Reflexes,    1nstin<t,   and    Kk\-»«is. 

Darwin:  Origin  of  Species,  ch.  viii,  1859.  Morgan:  .\nimal  Life  and 
Intelligence,  1891.  Jordan:  Footnotes  to  Evolution,  ch.  x,  \{UT2. 
Morgan:  Habit  and  Instinct,  189().  Morgan:  .\nimal  IVIm- 
vior.  Loeb:  Physiology  of  the  Brain,  P.MH).  Jennings:  'Hie  Bo- 
ha^^o^  of  the  Lower  Organisms,  1!M)L  Pornanes:  Mental  Kvo- 
lution  in  Animals,  1884.  Weismann:  The  lOvolution  Tlicory, 
vol.  I,  Lect.  8,  1904.  Loeb:  (leneral  Physiolog>',  vob*.  I.  II, 
1906. 

Chaptei{   XX.     Man's   Place   in    Natike. 

Darwin :  Descent  of  Man,  1n71.  llaeckel:  Evolution  of  Man.  2  vols., 
1883.  Huxley:  Man's  Place  in  Nature,  1S94.  Tyler:  The  Whence 
and  Whither  of  Man.  iS'.Ki.  Calderwood:  Evolution  and  Man'n 
Place  in  Nature,   189(1.     Keid:  The   Pres<'nt    Evolution  of  Man, 

1896.  Haeckel  and  (iadow :  The  Last  Link.  ls«»s.  Haeckel:  'Hir 
Piddle  of  the  Universe,  P.KH).  L<'  Conte:  Evolution  an<i  Us  Hala- 
tion to  Religious  Thought.  1S«)9.  Fiske:  lixcursions  of  an  Evolu- 
tionist, 1883.  MetschnikofT:  The  Nature  of  Man,  1  ^: 
Man's  Place  in  the  Uiiivers<',  P.MJ3. 


-f^' 


I  N  1 )  h:  X 


Actinocephalus  oligncanthtis  (illus.), 
216. 

Adaptation,  56,  327;  categories  of, 
328. 

Aid,  mutual,  369. 

Allen,  J.  A.,  136,  206. 

Altmann,  theory  of  protoplasmic 
structure,  250. 

Amaryllids,  sports  of  (illus.),  103. 

Arnblystoma  opacum  (illus.),  20. 

Amitosis,  252. 

Amoeba  eating  one-celled  plant 
(illus.),  31;  moving  (illus.),  30; 
"polypodia,  stages  of  fi.ssion 
(illus.),  31;  reproduction  of, 
213;  (illus.),  214. 

Amphimixis,  154. 

Analogy,  between  variations  in 
species  and  in  languages,  325; 
defined,  173;  in  wings  of  ani- 
mals, (illus.),  173. 

Anaphase,  defined,  256. 

Andrena,  nest  of  (illus.),  3S4. 

Andricus  caJijornicua,  galls  pro- 
duced by  (illus.),  342. 

Anemone,  sea,  with  algie  in  body 
wall  (illus.),  377. 

Anosia  plexippus  and  its  mimic 
(illus.),  422;  metamorphosis  of 
(illus.),  235. 

Antlion,  larv-a,  excavating  pit 
(illus.),  330. 

Ants,  castes  of  (illus),  3<)1;  com- 
mensal life  with  aphids,  374; 
communal  life  of,  301;  nest  of 
(illus).  392;  (illus.),  393;  .scM-ial 
parasitism  of,  375;  .symbiosis 
with  plants,  377. 


Apes,  anthropoid.  rl.'i.s.siti(  .lUon  of, 

451;  cars  of  (ilhis.  i,  171. 
A[)hi<ls.   rommens^il   life  \\ith   Mi.t"- 

374. 
Appendix  vcnnifonni.s,  of  kanpnrfKi 

and  man  fillu.s.  \.  179. 
Ai)j)l('.    hybridiz«'<l    mo.sair    Cillii.s.>. 

101;  .'Seedlings  f)f  tin*  Willianuc 

lOarly  (iliu.-^. ).  102. 
A(juiln  rltrysiitlns  (illu.s.),  4  1. 
Arbdcin,  e\(ra-ovat<>s  of  (illus. ..  jsl  • 

riridis,  regeneration  in  (ill  . 

282. 
Arcfuroptcryx   litfitHjrapftica    (illu.H. ), 

302. 
Ascaris     incgahtrephala,     sp»  • 

genesis  of  (illus.),  264;  ^ m 

265;     (illu.s.).    271;     var.     :.  . 

valens,  cell  divi^iion  in  (illu-    . 

258. 
Ascidian  (illus.).  42;  (ilhm.),  3tU. 
Asters,  defintnl,  254. 
Atavism,  1<»(). 
Australia,  rabbit  and  other  p!  i;:  ;•  - 

of,  (>5. 
Aythyn,  f;iinily  of  Villus. \  14.1. 

liani.'icle    (illus),    365;    nirlamor- 

phosis  of  (illus.),  234 
Harriers,  gt'ogniphic,  316;  intluencrti 

of  g«'ogniphie,  l'2S. 
linsrnnion  cntistrictor  (illu-H  *,  43. 
liasilarcliia     arrhippu»,     uxhw'uWn^ 

Annain  (illu.s.),  422. 
Hati-s.  11    W.  402. 
Hateson.  Win..  141.  147.  14S.  192. 
lilt  tick,  wingh^jw  (ilhm  \  351. 
Beavers  making  \\v»X^  (iUu0.),  4J7. 


ATI 


478 


INDEX 


Bechamp,  theory  of  protoplasmic 
structure,  250. 

Bee,  carpenter,  nest  of  (illus.),  384; 
mining,  nest  of  (illus.),  384; 
social,  384;  solitary,  383. 

Beetle,  California  flower,  apparent 
determinate  variation  in,  152; 
polygon  showing  variation  in 
pattern  of  (illus.),  152;  (illus.), 
153;  (illus.),  154;  variation  in 
pattern  of,  134. 

Beetle,  fore  leg  of  male,  of  water 
(illus.),  73;  long-horned  boring 
(illus.),  12;  (illus.),  41;  scara- 
beid  (illus.),  72. 

Bell,  R.  G.,  85,  142,  192. 

Belt,  Thos.,  402,  417. 

Berries,  Burbank's  work  with,  93. 

Berthold,  theory  of  protoplasmic 
structure,  250. 

Bethe,  A.,  428. 

Bionomics,  defined,  1. 

Biophors  of  Weismann,  251. 

Bird  of  paradise,  male  (illus.),  221. 

Bittern,  American,  young  of,  show- 
ing fear  of  man  (illus.),  436; 
showing  no  fear  of  man  (illus.), 
435. 

Blacksnake  (illus.),  43. 

Blastoderm,  228. 

Blastula,  228. 

Blindness,  in  fishes  (illus.),  180. 

Blue  jay,  nestlings  of  (illus.),  442. 

Bones,  homologies  of,  in  vertebrate 
hands  (illus.),  169;  in  verte- 
brate limbs  (illus.),  170,  171, 
172. 

Boyesen,  H.  H.,  451. 

Brewer,  Wm.,  201. 

Brittle  stars  (illus.),  14. 

Brooks,  W.  K.,  1,  57,  165,  197,  244. 

Budding,  reproduction  by,  215. 

Buffon,  theory  of  protoplasmic 
structure,  250. 

Bumble  bee  (illus.),  385;  communal 
life  of,  384. 

Burbank,     L.,    80,    90,    91,     195; 


scientific  aspects  of  his  work, 
101. 
Butterfly  fish  (illus.),  420;  Monarch, 
metamorphosis  of  (illus.),  235. 

Cactus,  hybrid  seedlings  of  (illus.), 
98. 

Calcolynthus  primigenius  (illus.),  36. 

Callorhinus  alascanus,  family  of 
(illus.),  440. 

Calotarsa  insignia,  showing  second- 
ary sexual  characters  (illus.), 
74. 

Catnponotus  (illus.),  391. 

Cankerworm  moth,  showing  sexual 
dimorphism  (illus.),  222. 

CarcJiesium  sp.  (illus.),  34. 

Cardinalis  Virginianus,  diagram  of 
variation  in,  136. 

Castanea  vesca,  variation  in  leaves 
of,  159. 

Castle,  W.,  192. 

Caterpillar,  parasitized  (illus.),  360. 

Cattle,  British  breeds  of  (illus.),  86. 

Cecropia  tree,  with  ants  (illus.),  379. 

Cell,  30;  egg,  224;  fission  of,  in 
salamander  (illus.),  255;  meto- 
tic  divioion  of,  described,  253. 

Cells,  different  types  of  (illus.),  29; 
sex,  218. 

Cephalopods  (illus.),  40. 

Ceratina  dupla,  nest  of  (illus,),  384. 

Ceratium  (illus.),  207. 

Cercopithecus  (illus.),  446. 

Chcetodon  vagabundus  (illus.),  420. 

Characters,  illustrations  of  acquired, 
198;  inheritance  of  acquired, 
196;  secondary  sexual,  72. 

Chestnut,  variation  in  leaves  of 
(illus.),  159. 

Child,  C.  M.,  252. 

Child,  w^ith  six  toes  on  each  foot 
(illus.),  147. 

Chimpanzee,  foot,  skeleton  of  com- 
pared with  that  of  man  (illus.), 
453;  plan  of,  compared  with 
that  of  man  (illus.),  459. 


iNi)i:x 


I7«» 


Chipmunks  of  California,  chuisifica- 
tion  of,  117;  (illus.),  11^. 

Chroniosonics,  (Icfmcd,  2.53. 

Cliri^sojHi,  e^^s  of  (illus.),  22(). 

Cicada,  variation  in  til)ial  spines  of, 
134;  septcTulccein,  variation  in 
tibial  spines  of,  136. 

Cladonoius  Immhcrlianus  (illus.), 
409. 

Classes  of  animals,  35. 

Classification,  dotermincd  hy  lioinol- 
ogies,  173;  of  animals,  33. 

Cleavage,  22S. 

Coccidiiim  liOwbii,  life  cycle  of 
(illus.),  352. 

Coccidium  ovijorme  (illus.),  21G. 

Cock,  white-crested  black  Polish 
(illus.),  81. 

Cockerel,  silver-laced  Wyandotte 
(illus.),  82. 

Cockroach,  egg  case  of  (illus.),  340; 
showing  variation  in  number  of 
tarsal  segments  (illus.),  149. 

Color,  in  animals,  398;  in  organisms, 
how  produced,  403;  in  protec- 
tive resemblance,  400;  in  .sexual 
selection,  400;  u.ses  of,  399. 

Coloration,  directive,  419, 

Colors,  warning,  410;  table  of  insect, 
405. 

Commensal  ism,  370. 

Communism,  309,  385;  advantages 
of,  397;  basis  and  origin  of,  395. 

Conditions,  primar}',  of  life,  38. 

Conjugation,  of  nodiluva  (illus.), 
220;  of  Vorticdla  nebidifvra 
(illus.),  221. 

Conklin,  E.  G.,  70,  199,  201.  203. 

Convergence  of  characters,  204. 

Cope,  E.  D.,  55,  197. 

Cordyceps,  growing  on  a  cater|)illar 
(illus.),  3()3. 

Corn,  showing  results  of  hybridi/a- 
•  tion,  194. 

Correns,  K.,  192, 

Coues,  E.,  24,  119. 

Crab,    fiddler    (illus.),    3.8;    hermit. 


comnicnHal  life  with  ixilyps 
(illuw.),  373;  (illuH.^  374;  im'ltt- 
inori>luwiH  of  (illiiM.),  2.'«. 

Cramer,  F.,  1 1. 

Crieket,  mole  (illu-s),  3Jl:   (illus.), 
345. 

Crotalwf  adnmnnteus  (ilhffi.),  10. 

Cni.stacea   and    their   larNu    (ilhin.), 
.%5;  para-sitic,  .'i58. 

Cryf)tomcrui  jnjtonirn,  atavistic  vari- 
ation of  (illus.),  100. 

Cucuinaria  sp.  (illus.;,  19. 

Cucumbers,  sea  (illus.),  19. 

Cuenot,  L.,  185,  191,  192, 

Cunningham,  J.  T.,  201. 

Cyanoritta     rristaia,     nestlings     of 
(illus.).  442. 

Cycle  of  life,  240, 

Cyclops,  maturation  in.  272;  niatuni- 
tion  of  eggs  of  fillu.s.),  203, 

Cyp.sclurus  (illus.),  3.'i5. 

Cyrtophyllus  crcpUans  (illus.).  401. 

Dall.  W.,  197,  205. 

Darbishire.  \V..  192. 

Darwin,  C,  9.  22.  4.S.  tiO.  <i3.  07.  '  - 

71.  70.  80.   137.   141.   VM,  2.>>, 

311,  KiO,  407.  40.S. 
Darwinisni,  defiruii.  48, 
Davenport,  C,  B.,  192. 
I)(>ath,  241. 
DeeapiKJ.  showing  extnionlin.Tnk'  n*- 

genenition  (illu.H.).  147. 
Det^r,  he.'ul  of.  shcnvinj;  variation  in 

horns    (illus.).    140;    hor--^    ■■'" 

interliK-k»il  (ilhis.>,  43S. 
Degenenition,   347;   hy  f|ui«'sr<'nrc. 

•MV.\. 

Delage,  V.,  29,  40.  252 

De.seent,  tlw'or}'  of,  10;  th^•^»ri<•^  ol 

control  of.  10^. 
Determinants  of  \N'einn>  •""   251. 

IX'velo|)ment.   224;    d  't    in. 

230;   einbr>'onir. 

mental.    244;    fir  in 

cml>ry«>nir     (ihiix.).     227:     of 

HtMinder  (ilhiM.).  240    of  Mon- 


480 


INDEX 


arch  butterfly  (illus.),  235;  of 
the  prawn  (illus.),  232;  of  silk- 
worm moth  (illus.),  236;  of 
swordfish  (illus.),  239;  post- 
embryonic,  234;  significance  of, 
232. 

Devilfish  (illus.),  40. 

De  Vries,  H.  H.,  54,  111,  114,  146, 
187,  192,  193;  work  of,  on 
Oenotheras,  157. 

Diabrotica  soror,  apparent  determi- 
nate variation  in,  152;  frequen- 
cy polygon  of  variation  in 
(illus.), 152;  (illus.), 153;  (illus.), 
154;  variation  in  pattern  of 
(illus.),  134. 

Diapheromera  femorata  (illus.),  412. 

Dickinson,  Sidney,    65. 

Didelphys  virqiniana  (illus.),  46. 

Dimorphism,  sexual,  221. 

Dimorphodon  macronyx,  restoration 
of  (illus.),  293;  (illus.),  294; 
(illus.),  295;  (illus.),  296;  re- 
mains of  (illus.),  291. 

Dischidia,  wdth  ant  colonies  (illus), 
378. 

Distribution,  geographic,  309. 

Dog,  pointer  (illus.),  431. 

Dogs,  prairie  (illus.),  383. 

Douglas,  N.,  79. 

Draco  (illus.),  306. 

Dragon,  flying  (illus.),  306. 

Drepanidae,  classification  and  dis- 
tribution of,  in  Hawaii,  124. 

Driesch,  H.,  278,  279. 

Du  Bois,  E.,  462,  464. 

Diirigen,  79. 

Dyticus,  fore  leg  of  male  (illus.),  73. 

Eagle,  golden  (illus.),  44, 

Ears  of  apes  and  man  (illus.),  174. 

Earthworm,  regeneration  of  (illus.), 
284. 

Eastman,  C.  W.,  292. 

Echinus,  cleavage  in  calcium-free 
water  (illus.),  280;  microtuher- 
culatus,  gastrula  of  (illus.)   279; 


microtuherculatus,  normal  larva 

of  (illus.),  275. 
Ectoblast,  228. 
Egg  cell,  224;  of  sea-urchin  (illus.), 

248. 
Eggs  of  Chrysopa  (illus.),  226;   of 

various  animals  (illus.),  225. 
Eigenmann,  C,  179. 
Eimer,  T.,  55,  197. 
Embryo,  human,  foot  of,  460. 
Emerson,  R.  W.,  452. 
Emery,  C,  394. 
Encasement  theory,  2,  249. 
Endoblast,  228. 
Epigenesis,  276. 
Epigenetic  theory,  3. 
Eretmoschlys  imhricata  (illus.),  43. 
Ergates  sp.  (illus.),  41. 
Erynnis    manitoha,    distribution    of 

(illus.),  310. 
Eutamia,  in  California,  classification 

of,  117. 
Evolution,    biologic,   6;    cosmic,   6; 

defined,    1;    factors   of,    48;    in 

philosophy,  2;  Lamarckian,  55; 

mechanism  of,  48;  orthogenetic, 

55;  Spencer's  definition  of,  5; 

the  unknown  factors  of,  115. 
Existence,  struggle  for,  57,  60. 
Exocoetus  (illus.),  335. 
Extra -ovates    of   Arbacia    (illus.), 

281. 
Eye,  human  (illus.),  462;  pineal,  of 

horned  toad  (illus.),  176;  pineal, 

of  lizard  (illus.),  175. 

Factors,  extrinsic,  in  development, 
245;  intrinsic,  in  development, 
245 ;  the  unknown,  of  evolution, 
115. 

Fauna,  316;  Bassalian,  323;  littoral, 
324;  pelagic,  323. 

Feeding,  instincts  of,  432. 

FertiUzation  (illus.),  267;  (illus.), 
268;  of  Petromyzon  fluviatilis 
(illus.),  219. 

Fishes,  adaptations   of,  332;    blind 


iMn:\ 


4v>t 


(illus.),  ISO,  JUl;  jlyii,^  (illu.s.;, 
.'^35;  migrations  of,  340, 

Fish  louse  (illus.),  359. 

Fission,  reproduction  by,  213;  (il- 
lus.), 211. 

Fitte.st,  survival  of,  62. 

Flatwonn,  regeneration  of  (illus.), 
285;  (illus.),  2.s«). 

Flounder,  development  of  (illus.), 
240. 

Flower  bug,  variation  in  pattern  of 
(illus.),  135. 

Flowers,  varieties  originated  by 
Burbank,  98. 

Focke,  192. 

Fol,  H.,  theory  of  protoplasmic 
structure,  250. 

Foot,  of  horse,  evolution  of  (illus.), 
177;  of  human  embryo  (illus.), 
460;  of  mammals,  hology  of 
digits  of  (illus.),  178. 

Forel,  A.,  394. 

Fossils,  17,  290. 

Fowls,  skulls  of  (illus.),  88. 

Friedenthal,  460. 

Frog,  male  carrj'ing  eggs  on  back 
(illus.),  73. 

Galls  (illus.),  341;  (illus.),  342. 

Galton,  F.,  165. 

Gasterosteus,  207;  cataphradus  (il- 
lus.), 209. 

Gastrula,  228. 

Gaudry,  A.,  298. 

Gauss,  141, 

Goddes,  P.,  1. 

Gelasimus  sp.  (illus.),  38. 

Genealogy  of  animals,  36. 

Generation,  211;  spontaneous,  12, 
212. 

Geography,  relation  of  species  to, 
311.  ^ 

Geology,  table  of  ages  of,  298. 

Georgine,  variation  in  inflorescence 
of  (illus.),  161. 

Geranium,  improvQinent  in  (illus.), 
103. 


(iiTiii  cfll.N,  tluHtrj'  of  the  jnirity  of, 

191. 
(iillx-rt.C.  H.,  :J03. 
Gill  .slitw  of  vertebrati'**,  179. 
CMX'the,  W.  von,  1.  4.S.  103,  289. 
Gongtflus  (jotujjflouitM  (illiw. ),  415. 
('lonimn  fnctoralf  (illu«.),  34;  (illiut.), 

2()1. 
Gorilla  (illu.s.).   l.^O;  face  of  (illus.). 

457;  head  of  (illus.),  457;  young 

(illus.),  458. 
Gray,  A.,  197,  320. 
Grcgarina  poli/morj)ha  (illus.),  210. 
Gregarinida-,  reproduction  in  (illus.), 

21(). 
Gregariousness,  380. 
Grus  amerirana  (illus.),  20. 
Grosbeak,     cardinal,     iliagram     of 

variation  in.  !3(i. 
GryUolaljxi  (illus.),  314;  (illus.),  315. 
Gulick,  J.  T..  123. 

Haa.<^e.  K..  423. 

Haeckel,  K.,  32,  197.  2*^0    l."?    UVl 

404,  MM\,  4(i7. 
Hair    covering    of    human    ombr>'«» 

(illus.),  174;  covering  of  Ku.v<ian 

dog-man  (illus.),  174. 
Hawaii,  cla.ssification  and  tli.»*tnbu- 

tion     of     Dn'panidii'    of,     124; 

distribution   of  land   snaih  of, 

123. 
Henneguy.  L.,  2*V0. 
Henslow,  (J..  124. 
Hennlity.    53.     103;    defuml.     10,1; 

laws  of.   1S4;   Mendrl'ti  law  «if, 

1H7. 
Herlitzkn.  279. 
nt'nnaphnHliti.'<m,  223. 
Heron,  flying  (illu.««.),  24. 
Hertwig,  ()..  27S. 
Hcterogenewij*,  54;  iheorirsi  of.  114; 

tlu'onk'  of,  15<). 
Jlipjxntarnia  rotr 

oi,  1.30;  \'jiriaii"ii  III  j'.i    <iw'i 

(illuM^.  132:  (ilhw  \  i:t:i. 
Hbp.  wild  .'ind  domr?«ir  'illus  \  89. 


482 


INDEX 


Holophrya  muUifiliis,  reproducing 
by  sporulation  (illus.),  215. 

Homologies,  defined,  172;  of  bones 
in  vertebrate  hands  (illus.), 
169;  of  bones  in  vertebrate 
limbs  (illus.),  160,  171,  172;  of 
digits  of  feet  of  mammals 
(illus.),  178;  of  tail  of  man,  179. 

Homo  sapiens,  454. 

Honey  bee  (illus.),  387;  brood  cells 
of  (illus.),  389;  communal  life 
of,  387;  pollen  carrying  leg  of 
(illus.),  388;  wing,  hooks  of 
(illus.),  155;  wings  of  drone, 
showing  variation  (illus.),  155; 
(illus.),  156. 

Hooker,  Th.,  65. 

Horse,  changes  in  foot  of,  in  geologic 
time  (illus.),  303;  evolution  of 
foot  of  (illus.),  177;  hybrid  of, 
with  zebra  (illus.),  183. 

Horses,  trotting,  heredity  in,  168. 

Huber,  394. 

Human  embryo,  head  of,  showing 
embryonic  hair  covering  (illus.), 
174. 

Humerus,  end  of,  of  various  animals 
(illus.),  462. 

Humming  bird,  male  and  female 
(illus.),  71;  Rufus,  nest  of  eggs 
of  (illus.),  441. 

Huxley,  7,  25,  26,  64,  197,  309,  426, 
457,  459,  460,  468. 

Hyatt,  A.,  197. 

Hybrid  colt  of  horse  and  zebra 
(illus.),  183. 

Hybridization,  88,  154. 

Hydra  vulgaris  (illus.),  35. 

Hyla  regila  (illus.),  344. 

Icerya  purchasi,  62,  64. 

Ichneumon  laying  eggs  in  cocoon 
(illus.),  359. 

Ichthyophis  glutinosus,  eggs  carried 
by  (illus.),  338. 

Icterus,  distribution  and  classifica- 
tion of  American  spepjes  of; 


128;  galbula,  diagram  of  varia,' 
tion  in,  137. 

Idioplasm  of  Nageli,  251. 

Imbauba  tree  and  ants  (illus.),  379. 

Inchworm  (illus.),  411. 

Inheritance,  exceptions  to  Mendel- 
ian,  193;  experimental  studies 
of,  192;  Galton's  law  of  an- 
cestral, 184;  modes  of,  181,  186; 
of  acquired  characters,  196. 

Insects,  parasitic,  359;  special  adap- 
tations of,  340. 

Instinct,  426. 

Instincts,  climatic,  436;  environ- 
mental, 438;  of  care  of  young, 
439;  of  courtship,  438;  of  re- 
production, 439;  terrifying,  431 ; 
variations  in,  442, 

Intellect,  443. 

Islands,  relation  of  species  to,  312. 

Isolation,  53;  biologic,  109;  geo- 
graphic, 54,  117;  physiologic, 
54;  sexual,  54. 

Jack  rabbits,  showing  variation  (il- 
lus.), 320. 
Jennings,  H.  S.,  429. 

Kallima  (illus.),  414. 
Kangaroo  (illus.),  339. 
Karyokinesis,  details  of,  explained, 

253. 
Katydid  (illus.),  401. 
Keeler,  C,  420. 
Kelvin,  Lord,  44. 
Korschinsky,  H.,  Ill,  114,  156. 

Lacerta,  diagram  showing  varia- 
tion in  different  species  of,  139. 

Lacerta  agilis,  regeneration  of  (il- 
lus.), 286. 

Ladybird,  Australian  (illus.),  62,  64; 
beetles  (illus.),  416;  convergent 
variation  in  pattern  of  (illus.), 
132;  (illus.),  133. 

Lamarck,  48,  55,  111,  196;  evolu- 
tionary principle  of,  196. 


IMjKX 


4^^ 


Lamarckism,  111. 

Lankester,  11)7. 

Laveran,  352. 

Laws,  of  science,  9. 

Lecanium  olvw  (illus.),  .%r). 

Lemur  jiirrijcr  (illus.),  -l/jf). 

Lepast,  inetauiorphosis  of  (illus.;, 
234. 

Lepomis  megalolis  (illus.),  17. 

Leplodcra  hi/nlina,  showinj^  .sex 
dimorphism  (illus.),  224. 

Leptothorax  emcrsoni,  nest  of  (illus.), 
393. 

Lepus,  species  of,  showing  dilTrr- 
enees  (illus.),  320. 

Lerema  accius,  distriljution  of  (il- 
lus.), 310. 

Lerncecera  (illus.),  359. 

Life,  duration  of,  240;  its  physical 
basis,  25;  origin  of,  42;  simplest 
expression,  25. 

Lilies,  Burhank's  work  with,  lUU. 

Lily,  improved  seedling  with  two 
petals  (illus.),  100. 

Lina  lapponica  (illus.),  194. 

Linckia,  regeneration  of  (illus.),  284. 

Linna?us,  14. 

Lizard,  common  (illus.),  IS;  y>ineal 
eye  of,  175;  regeneration  of 
(illus.),  2S6;  walking  (illus.),  22. 

Lizards,  diagram  showing  variation 
in,  139. 

Locust,  on  sand  (illus.),  401;  red- 
legged,  variation  in  tibial  spines 
of,  133;  (illus.),  13G;  seventeen- 
year,  variation  in  tibial  spines 
of  (illus.),  130. 

Locusts  of  (lalapagos  Islands,  .show- 
ing variation  (illus.),  'A\'.i. 

Loeb,  J.,  280,  428,  429. 

Loligo  pealii  (illus.),  40. 

Lophortyx  calif oniicus  (illus.),  15. 

Lucas,  428. 

Lyell,  C,  80. 

Macfarland,  F.  M.,  253. 
Macropus  rufu.s,  339. 


Malaria,  panuiitc  pitxlucinp.  352. 

Malthus,  67,  ttM;  law  of,  67. 

.Manunoth,  dntwing  of,  on  ivory 
(illuM.),  :«J7. 

•Man,  earlii-st  tnw.-.^  o|,  ;«J7,  4ii4; 
rmbrjology  of.  U'A).  Umtt,  nV.vU'- 
ton  of,  conipanil  with  iluil  of 
(■hiinpanze4*  (illus.).  453;  ^fiit^ 
alogj'  of.  AiWr.  I^'undertlial,  rtv 
mains  of  (ilhiH.),  465;  placv  in 
nature  of,  451;  plan  of,  coin- 
partnl  with  chimpan/,*'*'  (illtui.), 
459;  profilr.s  of  cmnin  of 
primitive  tyiM-x  af  (illu.H. »,  -Ul/li; 
nices  of,  }.')  I;  HuHsi.'in  tiog,  hiiir 
cov«Ting  of,  175;  Hkull  «if,  ciim- 
paretiwith  skull  of  oranx-utan, 
(illus.),  452;  fmrn  ."^py,  Mkull  of 
(illus.),  466;  stnioture  of,  453; 
tiH'th  of,  rompan**!  with  orang- 
utan (ilhis.),  454;  V(•^(i);uU 
structures  in,  461. 

Man  and  afM's,  ears  of  (illu.«<.),  173. 

Mantis,  praying,  eating  gniA.««hc»p|»or 
(illus.),  61. 

Marshall,  G.,  4 IK.  419,  423,  424. 

Mating,  cross,  lS<i. 

Matunition  in  cydops,  272;  of  ti:^;  of 
Cyclops  (illus. j,  263;  (illu!«.>, 
265. 

Mayer,  A.,  79. 

Mc('<M)k.  II..  .394. 

M(<Vacken.  I  .  192;  ex|xTimfntal 
work  in  hrnnhty,  191. 

.McCulIcK-h,  O.  ('.,  .369. 

.Mfchanism,  276;  versus  vitalism, 
2Jt'). 

Milnm  rfks  f(trnnrtt\iru*  bainin, 
acorns  d«"|H*sit«tl  in  trw  by 
(illus.).  4,32;  (ilhi«.).  4.34. 

Mt'latutfJus  jrmur-ruhrum.  variation 
in  tibial  spiueit  of  (ilhu*. ),  VM. 

M»l:»ph.i.'«'.  th'fin««<l.  251. 

Mendel,  (J.  J..  ls7;  uxpcriuu'ii'-  ?» 
h.  nnlity.  IS2. 

Mirniruilijt  nunua,  variation  in 
leaves  of  (illus),  159, 


484 


INDEX 


Merriam,  C.  H.,  117. 
Metamorphosis,    235;    of    barnacle 

(illus.),  234;  of  crab  (illus.),  238; 

of   Monarch    butterfly    (illus.), 

235;  of  silkworm  moth  (illus.), 

236;  of  toad  (illus.),  237. 
Micellae  of  Nageli,  251. 
Microzymes  of  Bechamp,  250. 
Mid-parent  of  Galton,  165. 
Mimicry,  421. 
Mind,  448. 

Mite,  itch  (illus.),  363. 
Mitosis,  252;  details  of,  described, 

253. 
Moenkhaus,  89. 

Molecules,  organic,  of  Buffon,  250. 
Monkey  (illus.),  446. 
Morgan,  146,  157. 
Mousefish  (illus.),  410. 
Miiller,  F.,  408. 
Mutation,  54,  131,  147,  187;  de  Vries 

theory  of,  114. 
Mutilations,  not  inherited,  202. 
Myrmecophily,  372. 
Myrmica  scahrinodes,  nest  of  (illus.), 

393. 
Myzostoma  glabrum,  fertilization  of 

egg  of  (illus.),  267. 

Nageli,  47,  55,  111,  197;  theory  of 
protoplasmic  structure,  251. 

Narcine  brasiliensis  (illus.),  334. 

Neo-Darwinism,  197. 

Neo-Lamarckism,  197. 

Newbigin,  M.  I.,  398. 

New  Zealand,  plagues  of,  65. 

Noctiluca,  conjugation  of  (illus.), 
220. 

Nomeus,  commensal  life  with  Phy- 
salia  (illus.),  372. 

Number  of  young,  225. 

Nyderibia  (illus.),  351. 

Octopus     (illus.),     40;     punctatus 

(illus.),  40. 
(Enothera   Lamarckiana,    de   Vries' 

work  on,  157. 


Oncorhynchus  tchaytscha,  egg-laying 
of,  59. 

Ontogeny,  211,  224;  factors  in,  244; 
first  stages  of  (illus.),  227. 

Oogenesis,  264. 

Opossum  (illus.),  46. 

Opuntia,  hybrid  seedlings  of  (illus.), 
98. 

Orang-utan  baby  (illus.),  455; 
skull  of,  compared  with  skull  of 
man  (illus.),  452;  teeth  of,  com- 
pared with  man  (illus.),  454. 

Organisms,  geologic  age  of  groups  of, 
299;  simplest,  32. 

Organs,  vestigial,  174. 

Oriole,  Baltimore,  diagram  of  varia- 
tion in,  137. 

Orioles,  distribution  and  classifica- 
tion of  American,  128. 

Ornithotomus  sutorius,  nest  of  (il- 
lus.), 444. 

Orthogenesis,  113. 

Ortmann,  A.  E.,  108. 

Osborn,  H.  F.,  115,  203. 

Ostracoderm  (illus.),  305. 

Ostrich,  African  (illus.),  45. 

Ovocyte,  defined,  264, 

Ovogonium,  defined,  264. 

Oxytricha  fallax,  reacting  to  cold 
(illus.),  428. 

Packard,  A.  S.,  197,  297. 

Pagurus  bernhardus  (illus.),  374. 

Paleontology,  289. 

Palo  Alto,  stoclc  farm  of,  103. 

Pandorina  sp.  (illus.),  35. 

Pangenesis  of  gemmules  of  Darwin, 
250. 

Papilio  cresphontes,  larva  of  (illus.), 
322;  chrysalid  of  (illus.),  409. 

Paramoecium  aurelia  (illus.),  33;  re- 
production of,  216. 

Parasites,  external,  348;  facultative, 
349;  internal,  348;  obligate, 
349;  permanent,  349;  tempo- 
rary, 349. 

Parasitism,  347. 


INDEX 


485 


arthenogencsis,  215;  artificial,  283; 

variation  in  animals  produced 

by,  155. 
asteur,  13. 

attorn,  in  animals,  39S. 
earson,  Karl,  185. 
elecanus    eryUirorhynchus    (illus.), 

20. 
slican,  brown  (ilhi.s.),  329;  white 

(illus.),  20. 
eneus  potimirium,  development  of 

(illus.),  232. 
eronea  cristana,  variation  in  wing 

pattern  of  (illus.),  148. 
dromi/zon   fluviatilis,    fertilization 

of  (illus.),  219. 
ha)ieus  mexicanus  (illus.),  72. 
tieasant,  Argus,  male  and  female 

(illus.),  75. 
hlegethontius     Carolina,     larva     of 

(illus.),  418. 
hrynosoma  blainevillei,  pineal  eye 

of  (illus.),  176. 
byla,  of  animals,  33. 
hylliwn  (illus.),  413. 
hyllopteryx  (illus.),  415. 
hysalia,  commensal  life  with  No- 

vicus  (illus.),  372. 
hysiological  units  of  Spencer,  250. 
iddock  (illus.),  39. 
igeons,  races  of  (illus.),  87. 
impla  conquisitor,  laying  eggs  in 

cocoon  (illus.),  359. 
ipa  atnericana  (illus.),  43. 
ipofish  (illus.),  415. 
itiiccanthropus crcdus,  462;  remains 

of  (illus),  463;  (illus.),  464. 
lanaria  Iwjtihris,   regeneration   of 

(illus.),  285;  (illusO,  286. 
lants,    living    symbiotically    with 

animals,   376;   number  of,    16; 

parasitic,  362. 
late,  L.,  77. 
lateau,  424. 
lum   and    its   parent    (illus.),    93; 

plumcot,  types  of  (illus.),  92; 

seedlings  from  (illus.),  92. 
82 


Plums,  Burbank's  work  with.  OJ 

Podocoryne  carnca  (illus.  j,  373. 

Polar  bodies  (illus.),  270. 

Polyp,  fresh  water  (illus.),  35. 

Polyps,  commensal  life  with  her- 
mit crab  (illus.),  373;  (illus.), 
374. 

Poppies,  Burbank's  work  with  Cil- 
lus.),  99. 

Potato,  Burbank,  91,  92. 

Poulton,  E.  B.,  408,  419,  423,  424, 

Prawn  (illus.),  365;  stages  in  de- 
velopment of  (illus.),  232. 

Preformation,  276;  theory,  249. 

Prenatal  influences,  167. 

Pressure  of  atmosphere  in  relation  to 
ajiimal  life,  40. 

Primates,  454;  cla.ssifieation  of,  455. 

Primroses,  evening,  de  Vries'  work 
on,  157. 

Prophase,  defined,  254. 

Protista,  32. 

Protophyta,  32. 

Protoplasm,  chemistry  of,  27;  phys- 
ical structure  of,  28,  247. 

Protozoa,  32;  parasitic,  354;  re- 
production of  colonial,  216. 

Pterophryne  histrio  (illus.),  410. 

Pterichthyodes  milleri  (illus.),  305. 

Pygosteus,  207. 

Pyrus  japonica,  seedlings  of  (illus.), 
95. 

Quadnimana,  458. 
Quail,  California  (illus.),  15. 
Quetelet,  140,  141. 
Quince,  Japanese,  seedlings  of  (il- 
lus.), 95. 

Radl,  E.,  428. 

Raja  hitwcidata,  egg  case  of  (illus.), 

337. 
Rambur,  13,  14. 
Rat.  kangaroo  (illus. \  13. 
Rattlesnake,  diamond  (illus.),  1(). 
Realm,  arctic,  318;  Australian,  322; 

holarctic,   319;   Icmurian,   322- 


486 


INDEX 


neo-tropical,  321;  paleotrop- 
ical,  321;  Patagonian,  322. 

Realms,  geographic  organisms,  318. 

Reason,  443. 

Recognition  marks,  420. 

Record,  Zoological,  14. 

Redfield,  C,  106. 

Reflexes,  426. 

Regeneration,  285;  of  blastula  of  sea- 
urchin  (illus.),  287;  of  earth- 
worm (illus.),  284;  of  eye  of 
triton  (illus.),  287;  of  flatworm 
(illus.),  285;  (illus.),  286;  of 
Hydra  viridis  (illus.),  282;  of 
lizard  (illus.),  286;  of  starfish 
(illus.),  283;  of  Stentor  caeruleus 
(illus.),  282. 

Remora,  commensal  life  with  shark 
(illus.),  370. 

Reproduction,  by  budding,  215;  by 
sporulation,  215;  excess  in,  58. 

Resemblance,  general  protective, 
406;  special  protective,  411; 
variable  protective,  407. 

Reversion,  166. 

Rhizobius  veniralis  (illus.),  366. 

Rhodites  rosce,  galls  produced  by 
(illus.),  341. 

Robinson,  L.,  461. 

Rocks,  sedimentary,  how  deposited, 
293. 

Romanes,  G.,  109,  461. 

Roux,  W.,  70. 

Riickert,  272. 

Sacculina     (illus.),    365;     carcinus, 

parasite  of  crab  (illus.),  358. 
Salamander,  blunt-nosed  (illus.),  20; 

cell  fission  of  (illus.),  255. 
Salix  auritax     purpurea,   variation 

in  stamens  of  (illus.),  160. 
Salmo  irideus  (illus.),  343. 
Salmon,  quinnat,  egg-laying  of,  59. 
Saltation,  54. 
Samia  ceanothi,  cocoon  of  (illus.), 

332. 
Sarcoptes  scabei  (illus.),  363. 


Scale,  black  (illus.),  366;  cottony 
cushion,  62,  64. 

Sceloporus  undulatus  (illus.),  18. 

Schaffhausen,  46,  464. 

Schistocerca,  species  of,  from  Gala- 
pagos Islands,  showing  varia- 
tion (illus.),  313. 

Schmidt,  P.,  346. 

Scorpion  (illus.),  331. 

Skulls  of  two  breeds  of  fowls  (illus.), 
88. 

Scutellista  cyanea  (illus.),  366. 

Sea  anemone,  anatomy  of  (illus.), 
36. 

Seal,  fur,  family  of  (illus.),  440; 
killed  by  parasitic  worm  (illus.), 
357. 

Sea-urchin,  egg  cell  of  (illus.),  248; 
larva  of  (illus.),  275;  regenera- 
tion of  blastula  of  (illus.),  287. 

Segregation,  53. 

Selection,  artificial,  51,  80;  artificial, 
its  relation  to  evolution,  106; 
claimed  importance  of,  50; 
natural,  57;  sexual,  51,  57,  71; 
sexual,  criticisms  of,  77;  sexual, 
experimental  stage  of,  79. 

Selenka,  460. 

Self-defence,  instincts  of,  433. 

Semper,  C.,  131. 

Separation,  53. 

Serpent  star  (illus.),  14. 

Scrphus,  carrying  eggs  (illus.),  340. 

Sex,  211,  220;  cells,  218;  determina- 
tion of,  170. 

Sexes,  numerical  relations  of,  170. 

Sexual,  secondary  characters,  72. 

Sheep,  artificial  selection  of,  81; 
Dorset  (illus.),  83;  Merino  (il- 
.lus.),  85;  polled  Welsh  (illus.), 
83;  Rocky  Mountain  (illus.), 
382;  Southdown  (illus.),  84. 

Shelford,  423. 

Silkworm  moth,  development  of 
(illus.),  236. 

Silkworms,  experimental  rearing  of 
150. 


INDEX 


ls7 


Silva,  car  mm,  167. 

Skate,  egg  case  of  Ix'irn  door  (illu.s.), 

339. 
Slime  mold  (illus.),  32. 
Snails,     distribution     of     land,     of 

Hawaii,  123. 
Solenop.fis  fuga,  nest  of  (illus.),  392. 
Species,   changing  with   space  and 

time,  IM;  estimate  of  duration 

of,  302;  number  of,  14;  onto- 
genetic, 114. 
Species-forming,  117;  by  saltations, 

156;  various  theories  of,  108. 
Spencer,  Herbert,  5,  196,  197,  198; 

definition  of  evolut  ion,  5;  theory 

of  protoplasmic  structure,  2.')(). 
Spermatogenesis  of  ascaris  (illus.), 

264. 
Spermatozoa  (illus.),  218. 
Spcrmatozoan,       development       of 

(illus.),  266. 
Spermatozoid,  261. 
Spha'rechimis  Echinus,  hybrid  lar\'a 

of  (illus.),  277;  hybrid  pluteus 

of  (illus.),  280. 
Sphoorechinus     granulans,     heating 

larva  of   (illus.),   279;   lithium 

gastrula  of  (illus.),  279;  lithium 

larva   of   (illus.),   278;    normal 

larva  of  (illus.),  275. 
Sphenodon,    pineal   eye    of    (illus.), 

175. 
Spider,   nest   of  trap   door   (illus.), 

346. 
Sponge,  simple  (ilhis.),  36. 
Sports,  186;  examples  of  race  formed 

from,  161;  species  arising  from, 

107. 
Sporulation,  reproduction  by,  215. 
Squid  (illus.),  40. 
Stamens    of   willows,    variation    in 

(illus.),  160. 
Stanford,  Leland,  103. 
Starfish,     regeneration    of    (illus.), 

283;  walking  (illus.),  23. 
Starks,  E.  C,  303. 
Stentor   coer ulcus    (illus.),    282;    re- 


acting   to    light     (illus.),    4:iO; 

reproducing  by   Jiiision   (illu.s.), 

215. 
Sticklebacks     (illus.),     209;     onto- 

gonetic  variations  in,  207. 
Sting-ray  (illu.s.),  333. 
Structures,     convcrgf'nce    of,    204; 

l)arall<'lisms  in,  204, 
Struguh'  for  existence,  57,  60. 
Strrithio  rnmrlu.s  (illus.),  45. 
Sunfi.sh,  long-eannj  Hllu.s.),  17. 
Sur\'ival  of  the  fittest,  62. 
Swift,  common  (illus.),  IS. 
Swordfi.sh,  development  of   (illus.), 

239. 
Symbiosis,     373;     of     {jjarits     and 

animals,  376. 
Si/ngatnus  trdchnlia  (illus.),  223. 
Systema  Xatunc,  14. 

Tamixi  solium  (illus.),  355. 

Tail  of  n)an,  hology  of,  179. 

Tailor  bird,  nest  of  (illus.;,  444. 

Tapeworm  (illus.),  355. 

Tarsiil  segments,  variation  in,  ccK-k- 
roach  (illus.),  149. 

Taxis,  282. 

Taylor,  Hayard,   163. 

Teeth  of  man  and  orang-utan  corn- 
pared  (illus.),  454. 

Telegony,  Kit). 

Telopha.se  defined.  2.56. 

Temperature  in  relation  to  animal 
life,  38. 

Termitophily,  372. 

Termites,  castes  of  (illus. \  395; 
conununal  life  of,  394. 

Terrifying  appearances.  418. 

Thnlrssn  (illu.s.).  'MW  ;  (illus.  1.  :MV2. 

Theory,  transmutation,  of  l>;imnrrk, 
lil. 

Timothy,  heads  of,  improvetl  by 
selection  (illus.),  91. 

Toad  (illus.).  344;  honntl,  pineal 
eye  of  (illu.**.),  176;  metamor- 
phosis of  (illus.),  237. 

Tobacco  worm  (illus.),  418, 


488 


INDEX 


Toes,  variation  in  number  of  (illus.), 

147. 
Torpedo  (illus.),  334. 
Tower,  W.  L.,  404. 
Toxopneudes    libidus,    egg    cell    of 

(illus.),  248. 
Toyama,  192. 
Trembley,  Abbe,  286. 
Tremex  columba  (illus.),  362. 
Trial  and  theory  of  behavior,  430. 
Trichia  favaginea  (illus.),  32. 
Trichina  spiralis  (illus.),  356. 
Trimen,  408. 
Triton,     regeneration     of     eye     of 

(illus.),  287. 
Trochilus    rufus,    nest    of    eggs    of 

(illus.),  441. 
Tropism,  282;    theory  of  behavior 

by,  428. 
Trout,    ontogenetic    variations    in,* 

208;  rainbow  (illus.),  343. 
Tschermak,  192. 
Tunicate  (illus.),  364. 
Turner,  L.  J.,  39. 
Turtle,  hawk  bill  (illus.),  43;  with 

two  heads  (illus.),  146. 
Twig,  insect  (illus.),  412. 
Two  Ocean  Pass  (illus.),  317. 
Types  of  animals  (illus.),  31. 

Uexkull,  428. 

Uncinaria,  parasite  of  seals  (illus.), 

357. 
Unity,  in  life,  12,  22. 
Urolophus  goodi  (illus.),  333. 
Use  and  disuse,  effects  of,  206. 

Variation,  131;  curves  of  (illus.), 
140;  Darwin's  laws  of,  137; 
determinate,  150;  determinate, 
apparent  example  of,  152;  onto- 
genetic, in  sticklebacks,  207;  in 
parthenogenetic  animals,  155; 
Quetelet's  law  of,  141;  in  wings 
of  honeybee  (illus.),  155;  (illus.), 
156. 

Variations,  acquired,  142;  congeni- 


tal, 142;  continuous,  146;  dis- 
continuous, 146;  in  function, 
19;  meristic,  148;  substantive, 
147. 

Variety,  in  life,  12. 

Vedalia  cardinalis  (illus.),  62,  64. 

Vegetables  originated  by  Burbank, 
98. 

Vertebrates,  earliest  remains  of,  305 ; 
gill  slits  of,  179. 

Vespa  (illus.),  385;  germanica,  vari- 
ation in  pattern  of  (illus.),  134. 

Vespa,  nest  of  (illus.),  328,  386. 

Vestigial  organs,  174;  explanation 
of,  181;  vestigial  structures  in 
man,  461. 

Vitalism,  276;  versus  mechanism, 
246. 

Volvocince,  reproduction  in,  217. 

Von  Kolliker,  111,  114,  156. 

Vorticella  nebulifera^  conjugation  of 
(illus.),  221. 

Vulpes  pennsylvanicus  argentatus 
(illus.),  21. 

Wagner,  M.,  108,  117. 

Wallace,  A.  R.,  76,  108,  197,  311, 

319,  402. 
Walnuts,    Burbank's  work   (illus.), 

96;  (illus.),  97. 
Warblers,  yellow,  distribution  and 

classification  of,  120. 
Wasmann,  E.,  394. 
Wasp,  social  (illus.),  385;  variation 

in  pattern  of  (illus.),  134. 
Wasps,  communal  life  of,  385;  social 

nest  of  (illus.),  328. 
Water  bug,  giant  (illus.),  340. 
Weismann,  A.,  68,   154,   197,   198, 

423,  425;  theory  of  protoplasmic 

structure,  251. 
Wesley,  J.,  452. 
Wheeler,  W.  M.,  424. 
Wheeler,  W.  W.,  394. 
Whitford,  C.  B.,  168. 
Whooping  cran3  (illus.),  20. 
Wiedersheim,  175,  461. 


IxNDEX 


489 


Wiesner,  theorj'  of  protoplasmic 
structure,  250. 

Willows,  variation  in  stamens  of 
(illusj,  IGO. 

Wilson,  E.  B.,  125,  126,  279. 

Wing  hooks  of  honeylx-'c  (illus.), 
155. 

Wings  of  a  drone  honeybee,  show- 
ing variation  (illus.),  155;  (il- 
lus.), 15();  of  animals,  analogies 
in,  173;  variation  in  pattern  of, 
in  Perorwn  cristana,  148. 

Wiiiiliemia  4-pustuIota  (illus.),  34S. 

Woodpecker,  California,  acorns  de- 


posited in  tree  by  (illua.;,  432; 

(illus.),  434. 
Woniis,  parasitic,  354. 
Wynuin.  J..  461. 

Xerophnllum  nmilt  (illiw.),  409. 

Youatt,  cSt). 

Zcl)ra,  hybrid  (if,  with  h«>n«",  I'^^ 

Zirplura  rrisfxiln  (illus),  'M. 

Zoogeography,  309. 

Zoya,  279. 

Zur  Stnus-sen,  O.,  279. 


(5) 


I 


^iiiiiliil 


t 


